In the side of the door is a little hole. An allen wrench goes through that hole to loosen the adjust. I forget what size allen and which way to move it but that's where it is at least.
When all the parts were new the springs and things would cause this to self adjust. You would simply press the button and slide your thumb off sideways and let it free return, then tighten the screw.
Today there is a scar from the set screw allong with corrosion on the parts so they dont move so easy.