This depends on how deeply serious is the injustice against you and your inner reactions. For example, on a 1-to-10 scale, how angry or sad are you (with a 10 being extreme pain)? If you are near a 10, then I would recommend a mental health professional who knows Forgiveness Therapy or who is willing to read one of my self-help books (such as Forgiveness Is a Choice) along with you. If your pain is in the 3 to 5 range, you might consider going ahead with that book yourself and let me, in my printed words, accompany you on the forgiveness journey.
For additional information, see How to Forgive.