Mac users : In Preference, go to Sound and set your default devices.
PC users: Launch Control Panel > Sound (under Hardware and Sound) and then right-click on the Playback and Recording Devices and set your desired devices as the default.
If you do not see the devices you want to use here:.
Select the desired speaker and microphone by clicking the downpointing arrow for each:.
The Skype for Business options window appears.
To do this, launch the Skype for Business app on your computer and click the gear.
Prior to every online session to you'll need to check that the microphone (Audio Device) and camera (Video Device) are working properly with the Skype for Business application.