You forgive for yourself. You let go of that pain or anger inside.
I have friends who carry it as a precious talisman inside for years. They become prisoners of their own hate or pain. Forgiveness is like taking the handcuffs off, not from the villain, from your own heart.
It's not an easy thing and time won't heal it either. It frustrates me every time I hear that lie...'Time is a good doctor.' I call bullshit on it. Time doesn't heal anything. If you sweep it under a rug or lock it up in a closet, it will just sit there. 
Solving it, getting rid of it and healing it, it's all in your hands. It's a choice, and it's work. It won't 'just happen'. Many don't know you can make your amends, forgive without ever seeing the person or letting them know. It's an internal process. If you want the validation, and you reached the comfort zone of facing them, by all means. It will only make you a better person, but you don't have to. You simply do it in your heart, let go and wish them well. 
It's freeing..... You breathe lighter.... and feel happier. 
Trust me....:-)