I see the utility he uses/used is called ManyCam.
So install and run ManyCam, then once it is running connect to it in OpenToonz.
Instead of selecting the camera from the dropdown select ManyCam
For my experience I didn't care for ManyCam but it worked and I would still use it if using my computers internal camera.
The external camera I purchased works great so I use that instead.
Speaking of which though... I haven't reconnected it since rearranging so need to do that ASAP.