The geometry adjustments are internal to the monitor. To access them, you need to (carefully) remove the outer casing and look around for the little pots (in my experience, they've either been on the rear edge of the analog board facing out, or somewhere along the sides, facing up).

Someone who knows more than I do would be better able to help, but this will hopefully get you started.

One word of warning, though: this is not for the inexperienced. You MUST be very careful not to touch any live circuits, as the voltages present, at the very least, will be extremely unpleasant.

Good luck!

c