Most chain drive lifts are bled by raising and lowering the lift without a load. Raise the lift ½ way and lower it, ¾, lower, all the way, lower. As you lower the lift each time, you should notice air exiting the system into the power unit reservoir. If there is a good amount of air in the system, you may need to add a little weight to the arms to help it come down, but you do not want to lift a vehicle to perform this task. If the lift is a direct drive system, most of them have bleeder valves on the top of the cylinder. Slowly unscrew the bleeder. Close the bleeder when no more air/bubbles are coming out. Do this on both cylinders. Thanks for reaching out Ed!