anger, resentment and hatred is forgiveness. Nobody can change the past. Nobody can change others.
It is relatively easier to work on oneself. Inner work undertaken with a positive attitude will yield enough ground for forgiveness. Genuine forgiveness is rooted in gratitude.
The realisation makes it easy to forget what they did, and to love them....
To make it a little easier to stay at the level of consciousness at which forgiveness comes naturally, some practices may help. One of them is the fire ritual. Write down all the resentment you have, resolve to replace resentment with love and forgiveness, and then burn the paper on which all the negativity had been expressed as a symbol of rooting it out of the system.
Another way is to meditate and, during the meditation, visualise the person you dislike.
Think of at least one good quality or virtue that this person has. Meditate on this virtue. Then visualise this person walking towards you, and you offering the person a flower with a smile.
The person is astonished, but see the way he grabs this opportunity to make amends. When you come out of this meditation, you are equipped to forgive. You are ready to face this person and turn a new leaf in your relationship.
During the meditation, you offered him a flower; when you meet him, you are ready to offer a hug.