This tool is something Jordan Peterson speaks about in his book 12 Rules for Life (Pillar tool 3.12) After having an argument with someone, split up and go to different rooms with both of you having the intention of thinking of at least one thing you could have done differently in the events leading up to the fight. Each person must think about themselves: what they, themself, could have done differently (not the other person). Be as honest as possible with yourself, and try to avoid blindspots and biases you might have.
This process can take just a minute or two, or it could take a long time. However long it takes, when both parties have figured out something, they meet up again and share what they came up with.
The point of this tool isn’t to try to change the other person but to find what you could have done yourself. When a husband and wife have an argument, when they can meet up and not place blame, but instead discover how the other person is willing to change themselves to improve their relationship can be a very powerful way of strengthening the relationship overall