My son learned and is still learning this. As Clemson’s closer the last few years (more of a fireman in 2017) he had to compartmentalize and focus pitch by pitch. All he could do was execute and move on. Not sure how much your son will read or reads but any Stoicism books along with Dorfman’s book in the mental game we’re all recommended reads by their mental coach.
At the end of the day he needs to be comfortable with being uncomfortable.