how do you set up the dev versions of a game?

https://www.google.com/logos/2020/kitsune/dev1/kitsune20.html
the link for the fullscreen of the dev 1 version of the game
the link for the normal version is basicaly the same except the "dev1" wrote part in the link; you can change the number with any from 1 to 11 to get a diferent version of the game in develoment state
the normal version uses it with "rc1" but number can be any from 1 to 7

thank you