I guess I am a veteran at this part. I have been hiding it for many years. It is hard. The best days I manage to not take frustrations out on kids. The worst - he gets biting comments to knock is ego down a few notches.
How? Deep breaths. I also made a list of reasons why I can not blow up and out. What are the positive outcomes to keeping my cool. And the repercussions if I do not.
This is new for you and the pain is fresh. If you feel yourself about to let go - take 10 slow deep breaths, the count backward from 20. And envision your list (or read it). And see if you are calm.
I also ask for exercise breaks. Get out of the confined space and walk about. Breathe.