Plex Has Over-ridden My Previous Movies Folder Metadata - How do I recover it?

The steps described in the Synology FAQ under repairing a corrupt database are worth a try because 1) the steps describe how to restore a backup database, 2) you may have enough things exactly the same as before (filenames, folder names) to make it work.

Have a read and if you have more questions, we’ll try to get ChuckPA or one of the other ninjas in here to advise.
Good luck!