I didn't find a manual, but from Microsoft's "How to use with Teams" web page (https://support.microsoft.com/en-us/topic/use-microsoft-modern-webcam-in-microsoft-teams-2eae0ef9-c27a-4ae7-8465-65c462e2afd4), here's how to turn on the mic:
If you want to use the built-in microphone, here's how to turn it on:
- Download the Microsoft Accessory Center app.
- Plug in your Microsoft Modern Webcam.
- In Microsoft Accessory Center, select Modern Webcam.
- Select Webcam settings, then turn on Webcam microphone.
If the link in the list above doesn't work, just go to the Microsoft Store (https://apps.microsoft.com/) and search for Microsoft Accessory Center