Are you bouncing at the trot or is the horse's trot too bouncy? If you are bouncing that is just timing, core strength and practice. If uts the horse then some horses have a short bouncy trot naturally and you just have to learn to ride it and gain strength and balance to handle it. Some horses bounce when they go slowly so lengthening the trot (making your horse go a bit faster but not too fast) can help smooth it out.
While your starting consider having someone holding you on a lunge as you trot around this way while your learning someone is controlling the trot . Try to shift your weight further back to keep your balance also h would watch so dressage riders and professional trainers on YouTube
It depends entirely on why the horse is bouncy. Is the horse unbalanced, or just expressive? If it's the former, that's something you can work on. If it's the latter, then that is something you need to learn to sit to, or consider another horse.
keep your horse between hand and leg (move your reins slightly left to right to left and right and keep your contact and keep your leg on