Rotator arm won't, rotate that is.

Okay, so the lower rotating arm won’t rotate, so I removed the outlet pump cover and got down to the drain and wash impeller. I need to get this off so I can get the screw I dropped out from under the pump. Anyway, how do I get the drain and wash impeler off. I removed the screw, and the impeller turns freely, but I can’t tell how to get it off/out. I would like to clean the filter screen while I’m at it but don’t know if there is one. Don’t see one in the exploded diagram I got off the internet. So that’s where I’m at, HELP!