I got my first review on RR?

It sounds like you need some distance. Sometimes when you're in the middle of writing your book (or drawing a comic for that matter), it's easy to overlook these sorts of errors; you've just been looking at it for so many exhausting hours of work that you can't see the problems any more. Happens even to professionals, it's why editors exist. In my day job, I help make books, and it's just a commonly agreed fact that you'll never send the first edition to print without at least one typo slipping through no matter how many people look at it!

My advice: treat this as an early draft. Thank the person for the review, be polite, tell them you'll take it on board, and just keep going, being mindful of the things they brought up. Don't bother going back right now if you can't find the issues, it'll only make you lose momentum.
Then after you complete the work, take a break to do some reading, research or training and start something new. Only revisit this work after you've had a good, long break from it and can look at it with fresh eyes. You'll suddenly see all the issues, and be able to tell which are really there and which were unreasonable nitpicks or fabrications. If you feel like you need to edit the text, you can do it then, or you can just leave it as your "old work" and focus on the new and say "hey, I was young and inexperienced! My new work is better because of the mistakes I made in this older one!". It's up to you really.

Sounds like that reviewer provided you with some constructive feedback - which is great thing. Constructive feedback is one of the things that enables the writers to grow.

It's actually very natural for writers to be in the blind spot and NOT to notice obvious things in their stories. Even distancing does not always resolve that problem, especially so if the writer has little experience in the field.

This is why it's recommended to have alpha reader and some beta readers, and then - if you can afford it - different types of experienced editors, who will help to professionally fix your story to eliminate as many mistakes as possible.

Good luck in your journey! 🧡

Honestly dealing with criticism is difficult and a skill you have to learn - not just the part where your ego is injured. I feel like most people feel a little defensive at first when they're criticised, it's only human. The really tricky part is maintaining a healthy balance between being open to it and the idea that the person criticising you may have a point and not blindly believing everything someone tells you because you doubt yourself or your story too much or in the name of "being able to take criticism".
In that regard, I'd almost say this is a fairly easy-to-process critique to receive. You and the reviewer agree on what makes a good story and what you dislike in a story (at least in some ways, I can only go off of what you've told us), so you can treat their review as a helpful one you can learn a lot from. (A less helpful one would be e.g. someone criticising you for having good demon characters because they expect demons in stories to be monsters or someone who prefers focusing on only one main character criticising you for having too many characters - you can still take away some things from reviewers like that but just have to keep in mind that they're not your target audience.)
I still get why it's overwhelming though. If I'd worked hard trying to get rid of all tense changes, reading through all my writing, and someone pointed out there are a lot of tense changes, I'd just feel overwhelmed tbh. The mere thought of doing all that work AGAIN, except I have to be even MORE focused and meticulous would suck the life out of me. (Then again I probably have ADHD so this is extra soul-crushing, mind-numin and mentally paralysing for me.)
In any case I'd also say either wait a while or get a beta reader. Maybe you can find a way to make proofreading what you've written enjoyable. I find that reading it out loud and pretending that I'm recording an audiobook is a lot of fun for me and it helps me notice more mistakes and improve the flow of my writing because I'm working with two senses rather than one. I also notice when I lose focus much earlier because it makes me stumble over my words and then I can re-focus.
But seriously, do this when you're in the right headspace for it. At the time of publishing this you were clearly not and that's okay. You don't have to be able to process and act on everything immediately. But you will be able to spot more mistakes when you find a good and fun way to proofread your writing and again, beta readers are a thing for a reason and I'm sure there are people who would really enjoy reading your story and helping you with it.
If the reviewer also criticised something about the content or style of the story and you don't know what to make of it, give yourself some time to reflect on it. Think about what the reviewer likes and dislikes in a story, what you like and dislike in a story, what you're going for and what expectations you're setting in the beginning of your story, and then go from there. Sometimes people read stories that aren't for them because they see certain key words (or even because of the platform a story is published on) and are vocal about their disappointment that the story doesn't meet their expectations. Sometimes the summary or intro of a story actually creates expectations it then doesn't meet. Just take your time, maybe wait for a few more people to comment and see if this one was an outlier or if there's a pattern. All you have to do is deal with the expectations you create in a satisfying way (that can include deliberately not meeting them by subverting a trope ofc), what other people with different preferences want your story to be isn't really your responsibility. (source: I once had someone completely rip apart my novel because they had a different sense of humour and expected fantasy to look different and demons to be bad. Still took away some valuable things from their critique but some points I just ignored. I don't think they took anything away from my criticism of their tone and repeated yelling. :D)

My suggestion is to have a program read your story outloud. If you have Word there is a read aloud function. If not you can try natural reader. Honestly, I ran into the issue with switching tense when I first started writing. Even after combing through my stories my readers found them. It was frustrating and demotivating. But it can get better. Over time, the more I wrote the more this issue started to go away.

So, I would suggest continue writing and edit when you can. Try the read aloud feature, because your ear will notice and since it's an AI they read exactly what is on the page while humans tend to replace words with the correct one without realizing it.

But most important just keep writing. The only way to learn is to keep going. Just because there are errors doesn't mean you don't have a great story to tell.

Oh, you're posting on RR too? Noice~ congrats on your review by the way. And keep in mind that don't get discouraged if the review is low. RR is a great website and getting criticism is good too to grow. Except for harsh reviews... Anyway, do your best!

So I actually looked for the review (I hope that's okay) and it does something I personally really dislike in reviews and that is only list negatives.
Personally, I don't think you have to do the feedback sandwich when giving feedback. But pointing out what a creator does well is important, not just to make the critique more disgestible to them emotionally (because I know there are a lot of "toughen up or get off the internet" kinda people who don't see that as a valid reason) but also because if you think a creation is overall good or has some appealing points and strengths to it as well and you don't tell the creator that, they don't get an accurate account of what your experience with their creation was. All they see is what you wrote, and if you only list flaws and things that bother you, you make it look like the creation wasn't enjoyable to you because it was that riddled with flaws. It also doesn't tell them what their strengths are and in what areas they should keep up what they're doing, maybe even refine it some more.
So it's no wonder the review was overwhelming to you. Personally I don't think it delivered its message in the best way. The reviewer probably found your story interesting and thought that it had potential, judging by the last paragraph, but they failed to convey that to you. So you basically got a lot of criticism all at once but no info about the overall impression people have of your story, if they ENJOY reading it despite some flaws.
Anyway, that's my take on it. You can probably still learn a lot from it but just keep in mind that critique isn't always delivered in the best way even if it doesn't outright attack you, and that if someone just lists a bunch of flaws and things to change, it might be that they just don't feel the need to point out the positives because those aren't things you have to change. Maybe it'll feel less overwhelming this way.(And I still think they should but that's just my opinion.)

Something I didn't really go into detail about in my first post about Royal Road is that there are a lot of things about the culture there that I don't... get. One of those things is the attitudes around giving and receiving criticism. Many people on there pride themselves on giving blunt criticism to the point where they think it's their duty to, even if its unasked for. While that's not the case here and the honesty is a good thing, on RR, this honesty seems to apply to negatives more than positives. I don't even think this reviewer is trying to be malicious. That's just kind of how things are over there.

A lot of people over there are very gung ho about receiving harsh criticism, like really wanting critics to go in as hard as possible on their story. It's to a point where it starts to feel like there's an expectation that everyone should be grateful for receiving that kind of criticism.

Don't feel bad about feeling bad about criticism, even if you agree with their points. The things they pointed out sound like mistakes I made when I first started writing seriously. Always make sure to have an understanding of the story you want to write in mind. If some of the criticism helps you achieve that vision, use it. If some of it doesn't fit for what you're doing, you don't have to take it.

That's great! I'm glad you were able to take some positives from this and not have it compromise your vision of you story as a whole.