if you can see bare metal, this one doesn't work.

if not, try this.  test it on small area first.

 make sure surface is smooth. use finish sand paper sand it if nessary. then clean and let it dry completely.  buy a can of clear coat from auto store and spray it.

3 years ago, someone droped a can of black oil paint on my dark green truck.  I used sand paper removed all black paint. and then spraied 2 layers clear coat. worked good for me.