How to play a forehead in tennis
Let's assume you are an adult and a right-hand player:

First, you do split steps, hold the racket with your left hand and put your right hand below your left hand on the racket
Second, when the ball just left the racket of your opponent, you rotate yourself so your body faces the right side of the court. Keep looking at the ball and your body steady in the process. You should bend your legs a little bit to lower your center of gravity.
You should find your racket on the right side of your body, now hold it loosely with your right hand using a semi-western grip, release your left hand and move it in the direction of the incoming ball. At the same time, step out using your left leg so the distance between your legs is a little bit wider than your shoulders, and keep your center of gravity on your right leg.
Now the ball starts to bounce and reach its highest point, you are going to hit the ball. You push your right foot to the ground and move your body weight from bottom to front, lower the racket head, and turn your pelvis from right to left at the same time. All of these powers combine into the force toward the front and your right-hand uses it to pull your racket from back to front and hit the ball right at the sweet point of your racket, keep pushing the racket until it reaches a limit where you cannot push any more and then release your racket and let the racket‘s inertia lead you from right to left. You should keep turning your body from right to left as well as moving your body weight from back to front until you body is fully facing your opponent and your body weight stands on the front of your left foot. Your shoulder will touch your chin if you do it right. your racket will be on the left side of your body without your control.