Re-linking to Catalog after pictures folders changed

Problem with Lightroom Classic Catalog after pictures folders changed

My Pictures are mainly stored in my OneDrive folder.  The Lightroom Catalog was also stored there, (but I was unaware of that).

The file structure of the pictures folders was then changed by me using Windows File Manager but not also reflected in Lightroom. I was unaware that changing the folder structure now meant that LR could not locate where its catalog had gone to.

Lightroom would then not start, saying the catalog was corrupted. 

I tried to fix problem by choosing to create a new catalog and merged it with the most recent LR catalog that had been backed up.

Lightroom will now open, but the catalog in Library says that it has 35,000 photo files that it cannot locate. Using “Find All Missing Photos” function does not assist.

Tried moving picture files in File Manager back where they originally were but, I cannot remember the exact folder structure before my changes were made; and I also get a message that these pictures folders or the Lightroom Folder cannot be moved as they are “in use by another application”.

The new catalog has references (numbers) of files but the thumbnails are blank meaning that they cannot be found.

I would appreciate assistance:

• To reconnect the original catalog to Lightroom (preferred); or
• To use the new catalog I created to find all the missing photos (which seems a difficult tor edious task).       Brendon