Regret is just information that showed up late. Read it, then use it.

Regret is unpleasant because it arrives after it could have helped, which makes it feel like pure punishment. Underneath the feeling is a clear statement about what you value and what you would do differently, and that statement is accurate in a way that is hard to get any other way. The timing is bad. The content is good.

When it comes up, write down the one sentence it is actually making. Then look for where that sentence applies to something still open in front of you. Regret that gets used stops circling.