1.Remove the sensor cover 

 
2.Pull up adjust knob on the regulator and adjust air
pressure to 3.5 or 4kgs (about 50psi).   

3.Use screwdriver to adjust air pressure sensor
to ensure 3.5 or 4kgs pressure will close the sensor.

4. Use meter to check.

5. Put the cover back, and adjust the input pressure back to 6~7kgs (about 100psi)