Oh now I see it there by the date and on the reverse at the end of CENTS. Now, it probably would go VF details if slabbed but these nickels are so common worn slick that I would be glad to be the owner of yours as it is.
There is the Verdi-gone product often mentioned here on CCF that might neutralize and remove most of that without harming the coin but it would be more logical to have other coins in mind to work on if buying a bottle.
I would just put this one in a airtite capsule to arrest and protect from further loss for now. Don't try cleaning it off otherwise.
It isn't going to melt away.