Edit: I've never looked into making a custom Android TV device either. I have a Shield but it could be cool to make my own with a Pi 5 or something for travel.
I mean, in the cas of Projectivity at least, when you launch Projectivity the first time it will ask you to change specific settings and it will take you to the corresponding menus. You just need to read the instructions and press OK. Sorry I can't be more specific at this time, as I am away from my TV.