I saw signs of frostbite coming on and I slathered on the vaseline and it helps a lot!
So I think you might wanna try that unless it's as black as coal and looks really icky!
Just leave it unless it's severe. My leghorns have a touch of it and after a few days of above freezing weather, it's almost gone. If it's worse, betadine or plain neosporin or both.