Notice the hand and head position. The keeper is over the ball, legs ready to take it to space. The ball will not deflect itself to safety by itself with hand protectors. Learning how the ball rebounds off your hands is part of the process. The process comes through training and repetition.
Tennis balls are good.
Get someone to help you out with a tennis racquet and balls. Have them set up around the top of the circle and whack tennis balls to your hands. You don't need to be in full kit, get your helmet, hand protectors, stick and pelvic protector and just take balls. Whether it be a hockey ball in full kit, or tennis ball in light gear, a keeper needs to learn through experience where balls will rebound to. That means taking a lot of balls.