The reason I posted a video and not advice: there's an exercise in the video that helps train the foundational skill of applying different force with each hand, simultaneously. In my lesson the other day, my teacher had me do a similar exercise, but with rhythm. I was trying to learn the rhythm while also playing the correct notes with the correct dynamics, and she told me to stop and work only on getting the rhythm into my body. She had me tap the rhythm on my body until it flowed correctly in time. Then I could add the notes.
The video demonstrates an exercise to help us physically internalize applying different levels of force at the same time. No notes, no phrasing, no dynamics. Just, what does it feel like to strike the legs more lightly with the left than the right.
In another video that I can't find, Garrick Ohlsson demonstrates how to voice the hands differently by striking the right hand harder, followed by the left hand (not simultaneously) more lightly. Then slowly close the gap between the hands, while maintaining the difference in force, until you can do both levels of force at the same time. If you want, you can alternate between the hands, harder on the left than the right, until you can more reliably separate and control the force activity of the hands.
Then add the notes back in, and the phrasing, and the dynamics.
Good luck!
