So, how do you undo it?
Tap Your data in YouTube (this is where Google hides advanced settings). unblock youtube user
A pop-up will ask you to confirm. Click Unblock again. So, how do you undo it
That’s it! They are now free to comment on your channel again. The mobile app is slightly different because the "Settings" menu is hidden behind your profile. unblock youtube user
Open the YouTube app and tap your Profile Picture in the bottom-right corner.