Pre Side Split is done by taking split position, but supporting it with the hands. Now you can switch to pan cake by sitting down and moving your upper body forward. Get back up again with the help of your hands, move your pelvis further down,and,switch to pan cake again. Repeat this process few times. In pan cake make sure you move upper body forward by tilting your pelvis forward, and not simply your upper body forward. If your mobility not good yet, you can work backward with your hands to support pre-split and then to sit down slowly. Try to leave your tilt point forward. As soon as you took pelvis forward, it's harder to keep Torso point upward, and then it's OK to rotate them forward as well, but keep your legs as much outward rotated as possible. Increase progression by simply going to deep with pelvis and abducting forward further