So in the 'choose-your-roles' channel there is actually a giant key attached to the tiny icons! Each icon has a sentence alongside it that explains what that channel is for. Reacting by clicking the corresponding icon will auto join you into that channel and thusly making it visible to you. The one you're looking for is going to be the slanted yellow tag icon [the 4th option]. Just click it and you should be all set! :)