There's a couple of ways to fix this. A new skin might be the easiest, if most expensive approach. Or, you can put a couple of rivets on either side of the hole (yes, fore and aft in this case). That will mess up the rivet spacing but will be safe. If you do this, flatten the bad dimple and drill out/deburr to remove the crack; then use filler to cover it up before you paint. Don't simply fill it with a rivet; that crack needs to be removed.
The other option is fussy but will leave you with a rivet in the right place. Flatten the dimple and drill out/deburr as before. Scuff the flange slightly around the rivet hole and the inside of the skin. When you assemble the skin for riveting, use Hysol adhesive to patch here. Before the Hysol sets, smooth it to match the skin (it's tough to sand later). When gluing aluminum like this, use naptha to keep everything really clean or the bond will tend to lift. When the Hysol sets, re-drill the rivet hole and countersink for the rivet. Sand the remaining Hysol to match the skin (if you smoothed it carefully and the patch hole is not large, you won't have a lot of sanding to do). Then, set the rivet. The Hysol should be sufficient bond to replace the rivet and, once painted, you won't know that the rivet isn't actually set into aluminum.
