The Noise Cancellation switch is located on the back of the right ear cup. By default, your headset automatically adapts to your surrounding ambient noise level. You can disable Adaptive Noise Cancellation and customize your own noise cancellation level in the Cisco Headsets mobile app.
1

Slide the Noise Cancellation switch down to NC to turn on noise cancellation.

Cisco Headset 730 noise cancellation switch
2

Slide the Noise Cancellation switch to OFF to turn noise cancellation off.