If you know the correct folder location, use the registry key mentioned in this article to tell Plex about it: [HowTo] An extended guide on how to move the Plex data folder on Windows
Be sure to read the caveat:
Beware! The path you type in must not include ‘Plex Media Server’ as last part.
So if now your plex data reside inE:\plex\Plex Media Server\, you type only
E:\plex\into the input field.