Hey!! idk if this is the best way to make custom tabs but sure is one of them, but basically i cant find a certain document with the lists so ehre you go! you can even costumize the build it tabs Fancy but basically head to your roblox studio files or this
C:\Users\Your name\AppData\Local\Roblox\Versions\newest version\RibbonConfig
after this just go the file and get the id!
heres a picture of mine
