As the home owner, you should be able to browse to: https://app.plex.tv/desktop/#!/settings/plex-home
Then edit the managed user, and add a proper name and save
After that, you can delete the user
As the home owner, you should be able to browse to: https://app.plex.tv/desktop/#!/settings/plex-home
Then edit the managed user, and add a proper name and save
After that, you can delete the user