From Finder, open your Documents folder.Open Finder by clicking on the Finder icon on your Dock.Change the name of the folder to something you'll remember, like Sims 4 Backup.
Right-click on the copied folder and choose Rename.Right-click on a free space and choose Paste.Use the following steps for Windows or Mac to back up and reset your game. If The Sims 3 does not load for you, make sure you use The Sims 3 folder rather than the one marked for The Sims 4.
NOTE: These steps also work for The Sims 3. Follow these steps to check for a corrupted save file or Gallery download in the Sims 4.