You need to lift the horses head upon approach to jump. If you physically can't pull their head up a couple strides before jump you need to try an elevator or stronger bit.
I would try giving a squeeze of your leg or a little kick. When other people are riding my horse, he likes to drop his head, so they have to nudge him on and they also lift up the reins a little. Hope this helps😊
It's a preventative for a horse that puts their head down. Hope it works for you!