I think that both a short run and longer run response would be helpful.

When the emotions come up, note that with interest, not judgment. Think “Oh, you are back again.” Look at them like a curious, nonjudgmental scientist would.

Have a plan for what to do when you find the emotions strong and/or you are ruminating. This plan would be some things that you can always or almost always do in the moment. It could for example be to meditate briefly: Stop. Take a gentle breath. Notice something with one of your senses. Have several of these in mind. Repeat as needed.

Write them on an index card and keep them with you.

In the longer run, making yourself stronger and healthier will make it easier to forgive. The more you have going for you, the less concerned you likely will be with negativity from the past. So I see kickboxing for example as a good idea, not only for release, but to help get closer to your most genuine, strong, healthy self.