Hello
There are different designs (described in the instructions).
You can loosen the brass cap on your compressor by hand against the clockwise direction.
When the cap is free, it can be pulled out and the valve opens.
After the function check, screw the cap back on by hand. The cap is secured against loosening by a rubber element.
How often you test the valve is purely a matter of feeling in my opinion. Every three to six months should be enough.