Click on your Apple menu in the top-left corner and select System Preferences.

Double-click the Sound icon.

Click on the Input tab to see your microphone list.

Click on the microphone you want to use. The Internal microphone is typically used in most cases if there is no external microphone.

Adjust Input volume by moving the slider to the right.

Click on your Apple menu in the top-left corner and select System Preferences.

Click Security and Privacy

Click on Privacy -> Microphone check if zoom.us is selected.