Uninstall with the KEEP option (first radio button)
Reinstall – HOWEVER
- Click “new or lost servers” (Plex Claim Token method)
- Click "Get Plex Claim Token hyperlink
- From the tab which opens, COPY the token
- Return to the installer tab
- PASTE the token in the box on the form.
- CLick NEXT - NEXT - DONE and let it install.
- If successful, it will report success and show “Claimed by: YourPlexUsername”
Ref:
For this to work, the only requirements are
- a valid connection from DSM → Plex.tv
- a valid username (account) to claim it with