In the top left corner of the screen, click the Apple logo and then select System Preferences.
On the window that appears, click on Sound to open the Sound Preferences.
On the next window, click Input if it is not already selected.
On this window, please make sure that the appropriate microphone is selected, then adjust the volume setting as needed. When the microphone is detecting audio, you will see activity for Input level.
When you are finished adjusting the volume, close the window.