Most likely you will be dealing with rust, hopefully it did not travel to the window post or other areas. You will have to remove the headliner and grind both sides of the damage. Contact one of the sellers in the swap meet section for a patch panel so you have an exact match and carefully trace out the area to be removed. Die grind and then tack weld making sure you do not warp the metal. There is lots of information on this process. Good luck!