The Rebbe's guidance on wrongs between people — asking forgiveness, forgiving others and making peace:
Ask forgiveness. When trouble strikes, examine whether one may have wronged someone, and seek their forgiveness (IK 5672); seeking forgiveness where needed is one of the practical steps that go together with prayer and Torah study (IK 1150). Sincere efforts to ask forgiveness are meaningful before G-d even when one can no longer reach the person directly (IK 5152). The true rectification for having embarrassed someone is to show that person greater respect and to improve oneself (IK 5863).
Forgive. One must forgive someone who sincerely apologizes — especially in Elul, when we ask G-d to forgive us (IK 3754).
Make peace — before Yom Kippur. Reconciliation and forgiveness are essential before Yom Kippur; resolving disputes promptly keeps them from growing (IK 5777). Making peace takes effort from every side: take the first step, and add to your own efforts to set things right (IK 4735). In Elul especially, use kind words and show compassion to others; harsh words have no place (IK 4713).
See also: Teshuvah – Rectifying specific wrongs; Teshuvah – Elul, Rosh Hashanah and the Ten Days of Teshuvah.