Start with a soft squeeze as a suggestion, then if your horse doesn't listen, kick, and each kick he/she refuses to move, increase power.
Keep using your leg off and on, don't use constant leg or you will get tired of it and so will your horse😄
Keep the hands a little in front of the saddle pad to keep them moving on and keep leg on:)
You should do transition work so for example for a warm up you can do a medium trot to a working trot, then after doing that a few times, let your horse have a rest (so a extended trot stretching). Then as their muscles warm up you can do a few faster transition so go trot - canter - trot or trot - canter -trot - walk - canter. Only ask the horse once or twice to move forward if they don't listen to you then use an aid to move them forward (your voice or a tap from the whip on their bum) . Do that for a couple of weeks and they should start to be more responsive to your legs :)
Make sure you don't nag the horse one squeeze and if it doesn't move forward you need to be firmer. Nagging doesn't help in the long run and the horse will become lazier and lazier.