I know that already.It doesn't pull out or turn up or down.It will turn about 1/16 of an inch if that. I know that already.It doesn't pull out or turn up or down.It will turn about 1/16 of an inch if that.

It must turn, if the knob pulls and pushes but won't, then it won't.
A screw pushes a spring, the spring pushes on a diaphragm, diaphragm sits on an adjustment port. No pressure on the spring makes zero pressure, turn the screw to add pressure to spring and diaphragm starts to allow pressure thru the port. This is the pressure regulator section, the same that won't allow pressure through in your unit.
The adjustment screw is the regulator knob with a lock feature against accidental misadjustments.
You brake, you pay? Some adjusters lock are seriously locked, ... It must turn, if the knob pulls and pushes but won't, then it won't.
A screw pushes a spring, the spring pushes on a diaphragm, diaphragm sits on an adjustment port. No pressure on the spring makes zero pressure, turn the screw to add pressure to spring and diaphragm starts to allow pressure thru the port. This is the pressure regulator section, the same that won't allow pressure through in your unit.
The adjustment screw is the regulator knob with a lock feature against accidental misadjustments.
You brake, you pay? Some adjusters lock are seriously locked, ...