Most skimmers have some sort of adjustable water lever (for inside the skimmer). Try and find that first. If not, more air means less water, and that may drop the internal water level a little.
Also, most skimmers have an optimal water depth they are supposed to operate in.
If your sump has adjustable baffles, you can try and lower the water in the skimmer chamber that way, or raise the skimmer by placing it on a stand.
In any case, the water inside if the skimmer should come somewhere close the the bottom of the collection cup, and allow a dry foam to build, then push up the inner section of the cup, then overflow into the cup itself.