In Synology Package Manager, uninstall Plex Media Server. Use the “Sign out and unclaim this server” option.
In Synology Package Manager, re-install Plex Media Server, using the Claim Token option. Additional screens will show you how to obtain and enter the token.
Then login to your server via the local IP address. Once that is successful, you can login via app.plex.tv.
Note: You need to be on the same subnet as your server. If you are remote, you’ll have to use a SSH tunnel.
