You will need both Technical and strength drills.
You should strengthen your core/torso strength, as that's where most of the movement is coming from, using drills such as squat, lunges, wall seat and more (you can see a good list here).
You will also need to improve your technical aspect of the movement (I assume you mean your carving of the snow with both legs - what's called: Parallel ski). There are some gym exercises with specific equipment that can help you master the movement.
I am a learning skier as well and generally that happens when I involuntarily lean, even slightly, back on turns especially when on harder slopes. Make sure you are turning in the correct position, you have pressure on the front of your boots.
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