Counter conditioning with very very high reward food - freeze dried liver works best, but any real pure meat is also effective.
Find the threshold for the dog at which she/he is still comfortable, and not yet stressed. For some it could be 60 feet while others just 3 ft. Be sure to know the stress signs - fixated pupils, whale eye, closed mouth etc.
At the closest calm distance, with the scary item (man) present, dole out the treats as fast as you can - no pausing to make as positive association as possible. Do this consistently when men appear, and the dog will ultimately associate good things happening with men.
It is also a good idea to have men, at the safe threshold distance, to throw the treats to the dog so that the treats are coming from the scary thing. The man should never make eye contact, stand to the side and always keeping the side of his body turned toward the dog, and toss the treats on the ground in front of the dog. With a lot of patience, the men can eventually move a little closer, closer and closer until ideally the dog is taking the treats from the mens' hand.