The object of this part of the game is to learn to control the parts of you that protect and propel you: primarily, your arms and legs.
The “how” is less important than the “why”: this part of the game teaches body control so you can comfortably sit still and upright for an extended period of time while meditating.
The “how” is entirely up to you and depends on your age and fitness. Pick a physical activity that you enjoy: anything from walking, bicycling, swimming (there’s a reason those activities constitute a triathlon: that’s a full body workout – but one you can adapt to YOUR pace!) Start by just getting outside for some fresh air! Move it or lose it.
If you want to prove to yourself that you CAN change and control your outer body, start with your toes. The darned things are as strong or stronger than your fingers! – yet we rarely pay much attention to them. Start by clenching and unclenching your toes into a “fist”, then use them to grip and pick things up. Make it fun and in short order, you’ll be surprised at the changes you’ll see in just your toes!