You can use any of these as a switch:
An external adaptive switch. Choose from a variety of popular USB or Bluetooth switches.
The iPhone screen. Tap on the screen to trigger the switch.
The iPhone FaceTime camera. Move your head to trigger the switch. You can use the camera as two switches; one when you move your head to the left, and the other when you move your head to the right.
Add a switch and choose its action. Go to Settings > General > Accessibility > Switch Control > Switches.
Turn on Switch Control. Go to Settings > General > Accessibility > Switch Control.
Turn off Switch Control. Use any scanning method to select Settings > General > Accessibility > Switch Control.
Bail out! Triple-click the Home button at any time to exit from Switch Control.