In UEFN, everytime you Check-in Changes, it creates a Snapshot, using the Snapshot History, you can load your map up to any snapshot made.
Then you can access it by clicking on Revision Control and selecting Open Snapshot History
Make a Snapshot now before you do, just in case, and enter something like grrrr or holy guacamole in the changelog,
You can copy from one snapshot and paste in another.
You may want to move your projects folder to somewhere else like C:\Fortnite Projects if OneDrive is the culprit, it often restores deleted content or makes a copy of stuff to where it once was.
You can set folder preferences in the Edit>Editor Preferences