Your friend and you both made a mistake:
- He invited you not only as a ‘shared user’, but as a ‘Plex Home member’.
- You accepted this invitation. Did you read the confirmation email/onscreen dialog in full?
You joined his Plex Home, which makes him your ‘master’.
If you want to be your own admin again, you need to leave his Plex Home:
Go to https://app.plex.tv/desktop#!/settings/users-sharing
Hold the mouse over the line with your user name.
There is a red X at the right end, which reads ‘Leave Home’.
