I was wondering how to revert to a older edit of a level?

Currently, I’m trying to make a project for my English class which involves animation. I was trying to decorate a current level when I accidentally put the settings to 160 trees in a space of about the size of a 2000 brush. And now whenever I enter the level, my frames drop really bad. So, I was wondering, how can I revert to an older edit without entering the actual level itself.

You might look in to backups in Saved\Backups if UE4 stored backup of that level, if it is then replace the file.

You might consider using version control for better backup solutions, in fact this version control primery function. You can use git as it does not require server to use it.