It is possible to switch to Focus mode in two different ways: 

- Using the Joystick button: 

Press Joystick button to switch to focus mode and twist joystick right and left to focus in and out (Press button again will switch to Zoom)

- Or using the F2 button:

Press F2 to switch to Focus mode and twist the joystick left and right to focus. Press F1 to switch back to Zoom mode. Note that you need to twist the joystick again to autofocus the camera and zoom out.