The first thing you will need to do is to make sure your layout is near perfect with a straight body and your arms go up Then you can do a couple of drills. One is to lie down on the floor and turn a 1/4 turn in a nice tight body with your core engaged ( pull the belly button to your back and squeeze your hips) Also you could jump and do a full turn without wobbling after it. If you have access to a resi pit above ground or stacked mats you can do jumps and pull your arms and do fulls to your back on the mat much like jump backs for back handsprings or jump up and back for standing tucks. The main thing to understand is that the dropping of the shoulder is what executes the twist so if you don’t use your arms it is ok. Just keep them up and turn your head the first time. You want to twist after the layout is executed. Some people think of it as twisting on top of the layout. It is at the point when your body is upside down in the layout and your body has come to your arms that the full occurs.
