Load a project save

Hi , I got a big trouble with the editor : I got a save of my map done yesterday ( the save I want to get back ) but today when I start my level the map was like in a old save from april ( 80% of my work in the level has disappear ) so I would like to come back to the save from yesterday.
I really need to know how to do that because its around of 120 hours of work erase if I can’t go back to the save !