I don't have an Ursa 12K, but normally to export an individual frame:
- Use the Deliver page to render out a single frame (set the timeline in/out point on that frame, and export it as a single 16-bit TIFF for example).
- Or, on the Color page, right-click on the frame in viewer window, select Grab Still, then right-click on the Still in the Gallery, export as TIFF for example.
- Or, if you want to export the frame as BRAW instead of TIFF etc, there's a button at the bottom of the RAW tab on the color page.