How to open / revert to a previous version of a Fusion design

Solution:

Use the following steps to open and (optionally) revert to a previous version:

Open a previous version

1. Expand the Data Panel in the top-left corner.
2. Navigate to the desired file.
3. Click the version button (for example "V10") to expand the version history.
4. Hover over the version that you want to promote and click the three dots that appear.
5. Click Open:

6. Continue with the following steps to revert to this version. 

Promote / Revert to the previous version

7. Open the file menu. 
8. Click Save As Latest.