My baby died 3 weeks after giving birth. How do I let go of the "what if"?

In this episode, Dr. Betters answers the question, "Recently I went into labor and had my baby at 33 weeks. He had to be flown to a larger hospital with a NICU and we stayed there for 3 weeks. I can't stop thinking about things I should have done so that I could have kept him in a little longer like I should have known to go to the hospital earlier and maybe they could have stopped my labor. It’s tearing me up thinking of the regret and the “what if”. I remember on one of your videos you said your wife and you dealt with something like this after you lost your son. How do I let go of the “what if”?"