I’d start by focusing on your grip. With the circle change, many pitchers shift their grip to the inside of the ball in order to make a tight circle with thumb and index finger. Don’t do that. There’s nothing magical about a tight circle. What’s important is just getting the index finger along the side of the ball so it can’t be used to accelerate the ball.
So, grip the ball with thumb and middle finger such that they cut the ball in half (turn your hand around so you can see your fingertips to check). Then put your index finger down the side of the ball only as far as your flexibility allows without shifting your hand on the ball. Finally, lay your ring and pinky fingers on the ball. There’s your grip.