I don't use it on the tablet.
I use it on Windows. I know the desktop version. You can download from the app. Or you can get it from the official website.
I have been using CSP since it was called Manga Studio. I have perpetual license 1.0 when it came to update 2.0 and onward. I just paid the Update Pass in Canadian its $40 a year and it auto updates beyond the free security updates and all the new features and versions.
When I wanted to update my plan from 1.0.
I had to log into the app and add in the new code I got for upgrading to the Access Pass. It came in an email once I bought the subscription. Think I used the icon on the menu that says USE ACTIVATION CODE.
Once I did that, it worked fine. There have been tickets for some, always having issues with updating on different devices since 1.0.
Other options are upgrades from 3.0 to 4.0 which you have to pay too. Or buy out a new 4.0 perpetual license.
The link shows how to update and get 4.0 using many options in a nice clean colour organized chart. Just go to the bottom.
https://www.clipstudio.net/en/news/202503/12_01/