Make certain that it is or is not attached. If not, physically move it to a better location. Turn down, not off, flow. If it has attached. Let it be for a while. If after a period it has not moved you can try and detach it with some very cold DT water, chilled in the freezer, and direct slowly, with a large syringe or turkey baster, at the base of the Nem to get it to detach and then move it to a better location.
Could you tell us about your system? How long has it been up and running? What corals are present? What are your parameters? We need more info to help make better suggestions.