How to remove corrosion of Aluminum from stainless steel fridge?

About a day ago, somebody took a sheet of aluminum foil and pasted it to stainless steel fridge using ONLY water (don't ask why). Now, there is a discoloration on the refrigerator that will not come off using different soaps/detergents etc.. I did some reading and it looks like the aluminum galvanized to the fridge...I think. So how could I get this off?