If you change your password, it unclaims the server (removes it from your account).
If Plex Media Server is running, you should see a Plex icon in the Windows Taskbar, in the lower right corner.
Double click on it. It should open a web browser to http://127.0.0.1:32400/web.
You should then be able to login, reach the server settings, and claim the server.
Alternately, see You need to reclaim your server, but don’t dare to touch the Windows Registry , and use Method 1.
