Practice.
Luckily you will get lots of it
Seriously - it starts small, with the little successes first. Nothing ground breaking. Just small areas that "I" can feel good about. If you try for the whole kabang all at once you will fail.
So how about recognizing what you can - you held out for 10 min instead of 5 min - you only swore at her twice instead of six - you were able to recognize how futile the argument was after she repeated herself the ninth time... .any small success.
What small positive change have you implemented?