How can I get my OBD monitors in my car to p smog inspection?

I had taken my car to get a smog check and everything ped except for the OBD monitor test. I not exactly sure what this is, but they said that all I needed to do was to drive the car for a few days and then the monitor would reset itself. I have been driving it for over two months, and it still will not p. What can I do? Is there another way around this?