How do I break in my catchers mitt square?

I want a square pocket on my catchers mitt so what's the best way to break it in square?

Wells inquires

my response:

In professional baseball the catcher's mitt pocket is broken in with a sledge hammer with a sawed off handle. They place the back of the mitt on top off a folded towel on a grass area off the playing field and hammer the pocket until they get the desired shape.