Finding the WDM-NF function in the menu of the AQ6317 series of OSAs does not work in the same manner as the other functions on the OSA. Instead, you will need to depress the ANALYSIS key on the front of the OSA, and then rotate the Data Entry knob. The menu choices you can rotate through will include the WDM-NF function.
This menu should be in all units which have firmware release version 2.0 or later. Please download the attached video for a demonstration of this feature.