Symptoms
When you are in a Skype call in Microsoft Skype for Business 2016, you may find you can't change the microphone or speaker volume by using Options > Audio Device.
Resolution
To fix this issue, install the December 4, 2018, update (KB4461545) for Skype for Business 2016.
More Information
After you install this update, you will receive a message that informs you that the change will take effect from the next call.