I tend to come up with titles by sitting down with a notepad and doing word association.
I think about what the comic is about, what the main character's name is, what a key object, place or plot thingy is called, and I'll write down every phrase I can think of, every pun, every random word or term...
I'm mainly looking for a few things. It needs to match the tone and genre of the story, it needs to hint at what the story is about, It needs to not already be the name of something else popular that would come up in a google search, especially in the same medium, and if possible, it needs to be easy to spell, so people can search it on a phone.
My old comic from my early twenties, Fan Dan Go, had a terrible title which inspired me to come up with the above rules. It was a meaningless nonsense title that tells you nothing about the story, and it was the same (from a search point of view) as a popular (at the time) cinema ticket buying website.
In the case of Errant, when I was thinking of ideas, I wrote down "Knight Errant" while coming up with all the words I could think of associated with knights (A big list with words like "jousting" "chivalry" "lady's favour" etc.). I looked at it... and then went, "...hang on." and just wrote "Errant" on its own, google searching it and searching it on Tapas like "No... somebody must surely have thought of this already..." but nobody had! It's short and easy to search (because it's an English word), it's clearly associated with knights, but as a single word title it feels modern, and because "Errant" means "out of place" or "gone astray" it gets across some of the comedy and character focus. As a title, I'm pretty happy with it.