From swinging facing the platform. As you arrive at the platform, place your feet on it and push your hips up so your body rises up. Let go of the bar and take the platform supports with your hand.
For a more advanced version, you can try to get up onto the platform without grabbing the platform supports.
You can find out more about this trick in my books:
Thanks to Fly'n Fit Trapeze School in Japan for providing a video for this page.