Hmm there are no easy answer to that one. I think the question is: can you forgive them or did they do something that you can't forgive given time?
But if you want to forgive even if you haven't been able to I'd say maybe try and keep a little distance to that person for a while until you start feeling less angry. Anger tends to come out, maybe as frustration and lack of patience which will probably be taken out on the person when you interact with them. It's difficult to control. But it depends entirely on the situation. The reason for your anger and if you think that can ever forgive them? If you think you can then time does help so keep some distance and let your anger cool off.
The best thing however is probably: If you feel that your anger is justified you should try talking to them and explain how you feel. If you feel like you may be a bit more angry than the situation calls for it could still probably help if you talk to them about that too as that could allow you to express your anger a little while trying to avoid hurting them. But it depends on if this is a person to whom you could talk to about these things.
In any case: something that often does help a little when having a problem is writing it down. Writing it down gives you perspective and although it does not solve your problem as such, it helps a little.
Lastly, these are just advices from me and is sort of how I would do it. So they are more inline with how I reason and may not suit you at all. Everybody handles anger differently so it does come down to what kind of a person you are. But if you like me is a rather non violent person, maybe this could help.