Adjusting barometric pressure on the autopilot

[j.fontana]

I have installed the 310 Redux on P3D v4 on Windows 10.
Having carefully read through the autopilot pdf document, I am unable to adjust the standard 29.92 pressure to another figure by using the rotary knobs. I am able to get this 29.92 figure registered on the autopilot screen (changed from a blinking value to a static value), but cannot alter it to the value of the position of the aircraft.
Thanks for any advice.

[j.fontana]

I discovered that it is movement of the smaller knob that adjusts the reading.