1.
Check if the app requires any permissions before using the camera. If so, grant those permissions.
2.
Check if the camera is enabled, and that the correct app has access to it.
3.
Test if the camera is working in another app.
4.
Restart the computer and video conferencing app
5.
Update the computer and video conferencing app to the most recent version.
6.
Reinstall the video conferencing app.
7.
Contact the video conferencing app support team if the above steps do not work.