IndexedDB: Persistent data lost; have backups

I have lost all content from an IndexedDB I had for a website that doesn’t store data online totaling some MB of content (I know because I have the backups I do periodically).
I have older IndexedDB databases that that contain all the data I have lost. Actually, I’d have to merge 4 databases already to get all data.
Due to the nature of the program, the data that the program has access to can just be merged together with no issues.
The problem now is that I don’t know how to merge all that data together, which would solve my situation.
Help please.