You can view previous versions of your project using the History feature.
Click on the History tab above the preview panel. In the All history panel, you can click on the history "slice" you need, and Download a project at this version if you need to retrieve a previous version. You can also then click the Label this version button (visible in Single version view) to give a label to a specific "slice", so that you can find it easily later.
Labelled versions can be accessed quickly via the History > Labels panel.
To exit the History mode and return to normal editing mode, just click on History again.
Note that when you copy a project, the history of that new project starts completely afresh—it's independent of the previous editing history of the original project.
If you click on the blue Compare to another version button in the top bar of the History view, this will bring up another view mode where you can drag some handles to choose the beginning and end point for a diff between any two history "slices" or labels. Then that view will update to highlight any changed files in the file list, and also highlight changes, colored by collaborator, in the source code for each changed file.
You can recover accidentally deleted files from the History view too.
On Free plans the History panel would show edits in the last 24 hours. If you need history from more than 24 hours ago, or if you'd like to test-drive the Full History feature as well as other premium features, you can start a free trial here . You can cancel your subscription at anytime.