The allen screw is for adjusting VTA, so it's not what you need now, but you can loosen it an lift the arm pillar up a a bit for better access (mind the wiring, though). So, you must remove the three screws. At least on some models, there is a hole in the black plastic cap for a screwdriver. If not, it can be done with an angled one, or a screwdriver bit held sideways in some suitable tool.