Tough life lesson here, but an important one:
If something isn’t working the way you expect, the right answer is to find out why. Check on Discord, ask here, etc. Any of us could have explained it to you. But if, instead of searching/asking for answers, you simply assume that the engine/editor is not working correctly, and instead manually try to force things to work the way you think they should work by manually deleting files, etc., then you are asking for problems.
The good news is that it sounds like you just need to re-import the assets; not the end of the world.
Also most of us solo developers start using source control when we learn the hard way what happens when we don’t. Again, if this is just a matter of re-importing assets, it was a cheap lesson. Check out Perforce. It’s a great and powerful solution for source control and works great with Unreal.
Good luck!