Learn to use your seat and legs to balance, and steer your horse. Practice on the end of a lunge line riding without your reins and practice finding your balance. Retrain yourself to sit correctly and tell your self seat, leg, hands when your wanting to turn. It is really a feel you have to acquire there is no way to explain it and it is easier said then done. Do you take lessons, if so your instructor ought to be giving you tips on what to do. If not maybe take a couple lessons and learn what a good seat feels like.
Try getting on bareback in a pen, using only a halter and lead. The lead is to remain over the horse's neck to get him out of a corner as they are inclined to go stand in a corner. Allow the horse to meander. If he stops tighten your calf muscles momentarily against his sides to see if he'll walk again. Just experiment with controlling him without your hands, or sounds. If you slump your back as you exhale and relax does he stop? You can't do him any harm. You do need to pay attention to what he does when you apply a particular signal.
^^ Linda Parelli's theory works well with a well trained horse of a calm nature in a tightly controlled situation. Not so well in many other situations. A horse can feel the change in balance and respond to that...or not.
It also won't work well with a horse who knows his rider likes to look around - like me. I'd HATE having a horse who turns right just because I look right. If I look back to see if a car is coming, or to see how other riders are doing, I do NOT want my horse turning! I also ought to be able to look at a sunset without my horse turning.
My horses will respond to my legs and neck rein. I don't need or want them turning without a specific cue. But that does not require me to be in their mouth. Someone who is in the horse's mouth too much usually is using the reins for balance, or hasn't figured out how a horse moves it head for balance. Those are things that can be taught on a lunge line, a round pen, with a bitless bridle, with slack in the reins, etc. It comes with experience, and there are multiple ways to get that experience.