I am sometimes successful at this; when I am, the script usually goes something like, "What am I worried/upset about? What should I have done differently? What can I do to prepare for this next time?" And then I actually talk myself through the things I could have done differently and whether they would have been successful, and if I hit upon something that would have worked, I try to identify a heuristic or plan that would help me do better in situations like these in the future. And do something to implement it immediately, if possible, or at least burn in into my head so I won't forget.

And if I don't hit upon anything I could have done that I think would have been a good idea, I just say to myself, well, that was just a bad situation. (Like if I happened to do badly at something because of luck, even though statistically, I'm pretty sure what I did was a good idea, even having updated on the evidence of it not going well once.)

This usually helps because if I keep worrying, I just ask myself, "is this a different concern I need to address, or is it the same just feeling-bad as before?" And then if it's a different concern, I do the same thing, trying to identify if this worry is actually a signal I need to think harder about the problem.

And if I really, truly decide, on reflection, that the worry isn't a useful signal, I find that really helps in getting it to go away. Because that way my worrying side feels vindicated, because the concerns have really been addressed; I'm not just forcing them out of my brain because they are worries and worries are bad, but because they are worries with no basis in reality. Once I actually feel confident of that, then I'm not worried anymore.

The trickier part, sometimes, is remembering to do this. I'm less sure about how to do that.