I know that I would have to create an account and put it at a rank that could change ranks in a group. I basically want it to promote someone if they complete something. So that if a user gets a certain badge(etc.), they would automatically be promoted in a group. How could I do this?
You will need to use HttpService, PHP, post requests, and you'll need somewhere to host it all.
May not work either way, but it might.
You can try to use this https://github.com/sentanos/roblox-js-server