Unknown extension 'Umap'

Umap will not open.

I have seen other posts about this but why is there never a clear answer? I was working on my project this morning. saved it, came back an hour later and now it won’t open my project. When I go to the content browser, my Umap is not there but the build data is. Then when I try to transfer the .umap autosaves I have, it is doesn’t show up when I try to add/import it and when I drag it into the content browser it just says

“unknown extension .umap”

This the second time I have posted something like this and never heard a response back, but now its for a school project so please can anyone help me?? I can’t lose this project.