At the top of any design category you click into (e.g. Facebook covers), you'll see two tabs: Made for you and Saved designs.
Made for you will be all your generated designs. And if you've ever clicked any designs in that category or edited them or downloaded them, they're going to automatically save in the Saved designs tab.
Note: Saved designs appear in a low-res format for fast loading, so they'll look blurry on the Saved designs tab. However, when you click into the editor or download them, they'll be high-resolution files.