1. Hold the hollow fist with both hands, and put the palm up behind your pectoralis major (underarm, move back as far as possible).
2, two heels together, toes open, in a figure of eight, (will you stand at attention?) toes don't move, heels open in a figure of eight, then heels don't move, feet are separated in a figure of eight (equal to standing at attention, feet move twice), at this time your toe distance is just flush with your shoulder width.
3. Start squatting naturally. I don't think 90 degrees is possible. I don't think it's necessary to do it at 90 degrees. I just feel that my thigh muscles are struggling. Do you know the posture of riding and the radian of legs? In addition, when squatting, the knees must exceed the toes.
I practice this myself.