Is this frostbite?

[Jo Anne]

 

[mechanic57]

Looks like it on the upper back side of the comb and on the tip of the highest peak of the comb in the middle.

 

[Jo Anne]

What should I do?

 

[21hens-incharge]

It looks to be very minor. I would do the following.
Do not rub anything on the injury as it can cause pain and bleeding.
It will heal in due time

Make sure the coop has good ventilation and keep the bedding dry to prevent additional frostbite.

That is really about all you can do. It IS a minor case so do not worry to much.