Go up to it at a walk, and just do different things, circle right in front at a walk and stop in front of it and come back around. Just change it up then try it at trot and canter and go back to walk again. The horse will then be more attentive to you, not worrying about rushing over the jump.
Evention tv on YouTube helped me with this problem x
Canter Poles before the jump, even just one is fine. Pops on a curve and straight line
Put 3 jumps in a row 1 stride apart jump the first and immediately do a circle to the right coming round back over it then immediately to the left coming back over it, then jump the second doing the same and then from the second jump the third and do the same thing, this really gets the horse listening to you as they will anticipate something else to happen instead of just running into jumps :)
One thing I used to do with my inexperienced thoroughbred is placing a ground pole one stride before the jump. Makes them think about they're distance and they're legs 🙃
Lots of jumps and lots of practice. Use ground poles and half halt a lot. Don't let it go too fast. If it does stop it make it stand a little before the jump and get up a trot before the jump. Stop the horse straight after if it's rushing afterwards. Do lots of exercise and flatwork before jumping. Hope this helps a bit 😊
Put ground poles on the ground before the jump and make him wait by half halts and only let him go at the last ground pole