If I am seeing the camera correctly, everything is pretty much there BUT the front glass element. This piece of glass has come out of its mount (the front ring with lettering on the inside rim) and is lost.
Is the focus mechanism moving? Without that moving, I would question if it is worth trying to replace the lens. If it is working-
I seriously doubt that you can find that particular piece of glass and be able to remount it. If the rest of the camera is in good condition, I would look for a replacement lens, full lens assembly.
Be aware that your lens is marked 7cm, not 7.5cm. I had a couple of Zeiss folders similar to your camera. One was marked 7cm and the other 7.5cm. There WAS a difference in the position of the lens board. Sometimes lenses are marked 'roughly' so a 7.5cm lens may actually be 7.8, etc. I would find a Duo 620 with a 7.5cm marked lens and get a measurement from the film plane to the lens board to see if this is an issue with your camera and lens search.
Finding a lens that will mount into a shutter like a Compur is not hard. But finding right focus position, proper shimming and adjustment, etc., can be tricky.
FYI, these cameras are on EBay (US) for not much money. Such as-
And it is not film tested as is. The release. Focus lever not working. The lens is clean and clear, with no separations, discolorations, scratches, fungus, haze as is the viewfinder.
www.ebay.com