Video opens with a camera not my computer camera.

[MarquitaWaters]

This just started to happen after I used an external camera.   I open zoom and you can't see me, just an option for a camera that is shown on the screen.  the options to change it are for that camera and another that aren't set up.  How do I get back to using my  computer camera. 

I have a meeting tomorrow and I don't have video now!!!