You help your dog change his negative mindset and view of the world. What if every time your dog meets somebody he doesn't like you feed your dog some high-value food like roasted chicken? Day after day he should start likely those people more and more. Dogs are pretty simplistic beings that form negative and positive associations. Unlike people though, they do not hold "grudges" or act out of vengeance.
Instead if they 'hate" people it's often a matter of people causing them to feel fearful or intimidated by them. This may be due to lack of socialization, a fearful predisposition or negative experiences (which may stem from things as innocent as the dog getting startled by people moving fast, coughing, sneezing or laughing loud).