Finally put the cover back on and replace the four screws you initially took out.
And that should be it for the pump. What was once an air pump should now be a vacuum.
Plug it back in and try it out at this point. Place your finder over each valve and see if you feel air being sucked in or not. It will be light but you should be able to notice it.
If you don't feel suction coming from both of the valves, dissemble the pump again and make sure you put the gasket and the gasket cover on in the right orientation and tightened the screws enough. You should feel suction come from each of the valves when assembled properly.