There are only two ways that I am aware that will solve this problem for you. The first is to bleach back the black mark on the print. The second is to retouch the negative. Both will require retouching the print as the final step.
I don't like bleaching out blemishes on prints. I prefer retouching negatives.
I don't use Spotone print retouch dyes for retouching negatives. I prefer to use red cocein (sp?) the dye can be diluted and built up over several applications. I use a 4/0 brush on a light table with magnifying glass or an Adams retouch machine instead of the light table.
The red cocein can be built up as I said earlier. It can also be washed out of the negative if the application is too heavy.
You will end up with a lighter portion in the sky where you retouch the negative (if this is the method you decide upon). So be careful in retouching the negative because it will go a long way to eliminating work for yourself when it comes to spotting the print.
Take time, work slowly, build up retouching in several applications...this can be learned and you can do it. Good luck.