I can't say for certain what you're looking for without seeing a picture of your regulator, but there should be some sort of knob or screw on your regulator that you'll need to turn. When you turn that, it should open up the flow from the regulator to the tank, and you'll see the pressure on the second gauge go up.
Editing some of the info from my comments into the answer: That screw in the center is what you are looking for. You'll want to tighten that, and that should start increasing the pressure on the other gauge. You may have to use a wrench or screwdriver to turn it to get it opening up. You will also have to turn the shutoff valve at the base of the regulator (the one with the little red handle) so it is in line with the tubing to open up the flow of CO2 from the output of the regulator to the tank.