The Sages (Rosh Hashanah 17a) have revealed to us a wonderful tool: "A person who forgives others who distress him and does not do or say anything negative in retaliation will have all of his transgressions forgiven." By removing your anger over the behavior of others, anger will be removed from you.

(Rabbi Eliyahu Eliezer Dessler; Michtav M'Eliyahu, vol.4, p.243)

Think of someone whom you have not yet forgiven. Let enlightened self-interest serve as a motivating factor to forgive that person.