I just let it go. Look at everyone here. Everyone does dumb crap or even hurtful things in their lives. I think unless you are an actual sociopath, it is impossible to not regret some actions, to not feel awful about some things you may have done in your life.
There is no need to stay stuck in emotions of regret or guilt about past actions. Make amends as best you can if that needs to happen, and move on. Move on with a determination to change that behavior, or not do that again. Or, if it is a really hard thing, commit to changing that thing slowly and incrementally over time. And be forgiving with yourself. We do the best we can with what we've got at the time. If you would forgive someone you care about for a thing, then you are obligated to forgive yourself as well.
The only outcome of regret and guilt is the theft of the present. It prevents you from being fully alive and fully responsive NOW. It doesn't relieve anything. It doesn't change anything. It doesn't make anything better. It can even actively bog you down in depression and freeze and stop you from making changes that could actually help repair past mistakes. Self-forgiveness and compassion can free you to make genuine amends and to repair relationships with others.
Basically, I believe if you would give compassion and understanding to another in the same circumstances, then you must afford yourself the same.