If you are going to tap it yourself, use a piece of lead, not a bucking bar, behind it. As you tap the metal, the lead will give a little. If you use a bucking bar, you will deform (stretch) the aluminum even more than it is now.
This is an area for a pro, if you want good results. If it is at the edge of the rib, there's probably not a lot you can do about it. The metal has already been deformed and you can not get it back to it's original shape. But, if you can get it pushed in, you can fill it, as others have said, and paint will cover it nicely. The other option is a new skin, which in the scheme of things, isn't that big of a deal. Besides, the old skin will get used for something before the project is over.
Good luck.