Haven't done this on the cobalt yet but there should be a bleeder screw that you need to back off to bleed the air out of the clutch slave cylinder. It is much easier with two people. First back off the screw a full turn or so and pump the clutch. When oil starts to bleed out, the screw needs to be tightened back down. Just repeat as needed until you have full pressure in the system again. It may be different with this car but mechanically, it should be very similar.