If your horse is good start to slowly post and sit in The back seat
Use your voice and half halt!
Half halt, keep your shoulders back and sit deep in the saddle.
Make sure your trot is controlled and at a nice pace before you ask for a canter and your reins are collected and then if he tries to speed up half halt and sit deep in your saddle
Hope this helps😊
Lean back and sit deep in the seat
Try to teach them words, my horse knows the word 'slow down' it really helps, especially in canter!
half halt and tighten your core. make sure you are not leaning forward. squeeze and release the outside rein (but maintain contact with the inside rein).