Swing out and back to the platform. As you swing forwards again, you need to make three kicks with your legs - forward, backwards and forwards again. These should be timed so that you kick backwards as you pass the bottom of the swing. As you reach the peak, with your legs still moving forwards from the last kick, let go of the bar and grab your knees. You will make a back somersault before landing in the net.
You can find out more about this trick in my books: