Make sure Plex Media Server is running. On some WD NAS, Plex Media Server may not auto-start after an update. See Plex inoperable after upgrade to PlexMediaServer-1.41.8.9834-071366d65-WDMyCloudDL4100_OS5.bin.
Then point a private/incognito web browser window at the IP address of the server.
For example, if the IP address is 10.1.2.3, use http://10.1.2.3:32400/web (you may need to use https).
See if you can login and reach server settings.
Note: If you changed your Plex account password, then your server is unclaimed. You will need to re-claim it before streaming to Plex clients.
