By leg, I mean calf, not thigh.
Lean back a little and aquezzs your thighs to the saddle and keep your eyes up. Good luck:))
Training your horse to listen to your seat doesn't happen overnight. You have to train that every transition between gaits comes from your seat. I like to initially couple the transition aid with breathing out (loud) as well as squeezing my thighs, sitting deep in the saddle and a slight pull on the reins until the horse understands the aid. Soon with repetition the horse will associate breathing out and squeezing your thighs with downward transitions and you won't need to pull on the reins, only maintain your contact to keep the horse soft in the transition. Hope that helps
Don't bring your leg foreword as you leanback tjo
Sit up tall and sit deep in the saddle. Tense your core muscles and squeeze gently with your thighs.
You need to pull back your arms, sit deeper in the saddle and slightly flex muscles.