Have you tried:
This happened to me about a week ago. No one could help me get it off- not even anyone at Roku after I finally reached a human to talk to. I cut off my Roku account. No sense having it if all I can see on all my tvs is guest mode screen!
Did you see the reply before yours? https://community.roku.com/t5/Solving-playback-issues/Stuck-on-guest-mode-and-this-sucks/m-p/1018668...