Try this daily. Let someone off the hook. Start with little wrong, a forgotten returned phone call, a missed appointment, and so forth.
Give the person a "do over." In golf it's called a Mulligan. They are free to try again.
Respond with, "hey no problem, I forget things at times." Or, "Oh, I understand."
Meekness does not equal weakness. We can be strong and forgiving at the same time.
These small acts of quick forgiveness lead to an easier time at being quicker to forgive others, including ourselves.
Life is too short to be locked inside a room of resentments. A room created by an unforgiving heart.