Breathe and count. Practice and work with a coach who hekps you feel confident and helps you improve your riding.
be confident with yourself and trust your horse. every solid relationship is built on trust. you are counting on your horse to take you safely over the jump as much as he is counting on you to believe in him!
Remember to breath. Count your strides up to the jump. Think of a your goal you have and think of how you are gonna get to this goal.
The more you practise the more confident you are also when in the area or warming up stay calm to keep your horse mellow and take deep breaths
Remember to breathe. Sounds so simple but really calms your nerves and can relax both you and your horse.