Speaking as someone who personally hasn't seen you ride, filming yourself is a great place to start. Make sure your not throwing yourself forward and trying to jump the jump for your horse (this actually makes it harder for them), but your position is only as forward as it needs to be, and your weight is in your heels.
said, but you also want to bring your body forward, and not down (I don’t know if that makes sense) so instead of throwing your shoulders at your horse, rather ‘lean’ into it. And keep your chin up!
Doing the jump position over poles
I would say filming your position would be a good place to start
Also with two point at the trot and canter fold as if you are going over the jump for 10-15 seconds to help with balance in the position
In addition, work on two point in the trot and canter! This makes you just focus solely on your position. Then, go over a jumping course and set the poles on the ground
Riding without stirrups to get your hips open and seat more secure and before jumping have few laps in all paces standing up in your stirrups to get your leg on and make it more secure
Also when jumping think about folding your body instead of standing up in stirrups. Usually you want your stirrups length to get a 90 degrees angle of your leg however that is way too short for me so I go a hole shorter (its up to you). Obviously stirrups should be a bit shorter than for flatwork to help u fold and pick yourself up.