Regain Plex Admin after accepting invite from other Plex user

[OttoKerner]

1. You need to leave his Home again, using the red X at the end of the line with your username/email under ‘Users & Sharing’
2. ask him to invite you again, this time only using the button ‘Share Libraries’ and not ‘Invite Home User’
3. give him access to your libraries by clicking on his line under ‘Users & Sharing’