Right click the small speaker icon usually found in the lower right screen corner.
A 4 or 5 item menu window should appear.
Work your way through each of the choices and further more into the subsequent windows, tabs, and properties.
There are many and nested one inside the other. Take your time and if confused or lost - "Cancel" is your friend.
For the most part, my sense is that some recent install or update may have changed the default microphone away from the cam mic.
Do not change anything at first. Simply explore and take notes.
Then go back and change anything that is or seems to be misconfigured.
Change only one thing at a time so you can easily go back and undo some change that caused another problem.