For Windows 7/8/10 PC:
1. Right-click on the in the task bar → Select Playback devices or Sounds.
2. Go to Playback tab → Double click “Avantree CF3001” → Select Levels → Apply Microphone as below.
Monitor function is only the computer feature of windows system, Apple OS system can't support monitor feature. If you want to monitor the microphone input in realtime through Mac computer, firstly you need to turn on any recording software (Audacity for example), make sure that the software supports voice Playthrough function otherwise you can not hear any sound when you speak to the mic. Setting as bellow:
Click Audacity menu à Click and open Preferences… à Click Recording à Select Software Play through: Listen while recording or monitoring new track à Click OK button