Bug/Issue Lost Saves

I play Stardew Valley on a Mac and I was playing on the multiplayer beta hosting a server when I decided to get off at the same time as my co-op farmer. The game didn't actually quit when I thought it did, and the game kept advancing with me passing out. When I finally got back it had been 3 years in the game.
Does anyone know if I can use my co-op partners save to restore it back to the original save I wanted it to be?
Please help me.
Thanks