It is difficult and sometimes frustrating, however you can practice on the land laying on your back, then move into the water and hold the wall, then move off the wall and use some type of floaty to hold you up, then ditch the floaty. Also if this doesn’t work and you cannot get it down, you can grind through using a giant stride/flutter kick variation.

It's all about flexibility and coordination. Look up some hip flexor and leg stretches and do them religiously. Then watch some YouTube videos on the eggbeater technique and practice on dry land, just laying on your back , then practice in the water while holding the wall… then progress to timed sets in the water.