1st Make sure your water height is correct per the manufacturer's specifications.
2nd you are going to need to slowly and carefully adjust the skimmer.
The reaction chamber of the skimmer generally has two states: active and non-active. When it is active the bubbles build and skimate is deposited in to the collection cup. After the skimmer has processed everything it can out of the water the bubbles should lower until the DOCs in the water increase enough for it to go to the active state again.
I recommend you start with it wide open and slowly, 1 notch every hour close it up until you just have the bubbles reaching the top of the neck. Then from there adjust it 1/2 notch every 12 hours until you are collecting the type of skimate you desire. If you do it correctly the first skimate you get will be fairly dry, and very dense. 12 hours later you will probably not be skimming any more and will have to adjust it closed 1/2 notch. You may get little to no additional skimate over the next 12 hours. Keep waiting at least 12 hours between adjustments, and when you thing you are only 1/2 notch away from being where you want to be empty the collection cup so you can see exactly what you get over those 24 hours. If you still want to skim off adjust it empty the cup and go another 1/2 notch for the next 24 hours.