Pray the prayer of forgiveness
Once we make the decision to forgive, we need to take action to put that commitment into effect. Perhaps the most effective way to do that is to verbalize our forgiveness to the Lord.
Acts 7:59-60 And they stoned Stephen, calling upon God, and saying, Lord Jesus, receive my spirit. And he kneeled down, and cried with a loud voice, Lord, lay not this sin to their charge. And when he had said this, he fell asleep.
When we declare to God our decision to forgive the person who hurt us, we recognize that it is primarily to Him that our commitment is made. In biblical terms, we establish a covenant of forgiveness with God, knowing His declaration that once such a covenant has been put into effect, it cannot be broken (Galatians 3:15).
From that point, our forgiveness of the offender is a spiritual reality. No matter how we might happen to be feeling about that person at any particular time, the fact that we have forgiven him or her means we will treat them as forgiven. (Part 4 of 6 Five Steps To Controlling Your Anger by Ronald E. Franklin)