From a quick look at our logs, it looks like you have two different accounts, one at https://glitch.com/@liam19789123456 which seems to be the one that you’re working with right now but that doesn’t have a GitHub account associated with it and https://glitch.com/@liam19789 which has your GitHub account associated with it.
A single GitHub account can only be associated with a single Glitch account, so if you log into the former account you should be able to use your GitHub account without any difficulty. If you’d like to see something else happen with these accounts, please let us know what you’d like to see and we’ll see what we can do to help.