Hi Niven,
The head bobbling works automatically for the first person character.
You can adjust its vertical and sideways movement using these API's :
#Camera.bobspeed = 0-2; **NEW** use the 'Set or Change a Variable' and the name of the camera
#Camera.bobUp = 0-2; **NEW** use the 'Set or Change a Variable' and the name of the camera
#Camera.bobSide = 0-2; **NEW** use the 'Set or Change a Variable' and the name of the camera
- here Camera is the name of your FPS Camera node.