Two ways, either:
Route 1: A bot that gives the role after typing the command/keyword.
Route 2: A bot that auto-gives a role and removes it after being verified.
(Main perk for this is you'll be able to prune members for inactivity if you don't have self-assign roles.)
Note: Putting the Send Message permission to NEUTRAL in the other channels will allow you to have a functioning MUTED role. (Muted role has Send Messages permission DENIED on ALL channels.)