First thing that you should do is grab a tablet driver for your new tablet (either official Wacom driver or OpenTabletDriver if you want further customizability).
And then, you should search for tablet area that you can reach all four corners at, and also comfortable for you to move through trial and error! (also make sure the tablet mode is set to "Absolute" mode instead of "Relative" mode if you do use OpenTabletDriver) make sure to set your osu! in-game settings at 1x or things will get weird
And that's all! You're pretty much done setting up your tablet, you can now start getting used to your new tablet, make sure you are playing easier maps than you used to play to get the fundamentals down and be patient since you might play worse compared to when you were using mouse, goodluck!