To change the microphone or speaker that InsiteVR uses to help you talk to others during meetings, click the Options icon on the bottom toolbar.
Then click the Meetings tab.
The first dropdown is to change your microphone - the source of audio input used so others can hear you. Select the one you'd like to use.
The second dropdown is to change your speaker - the audio device used to play back what others are saying during a meeting. Select the one you'd like to use.