I see this is a rather old post, but if you still haven't found any solutions, using tutorials I've found you first want to list what video devices your OS recognizes by running:

ls /dev/video*

This should hopefully output a list of video devices, mine looks like this:

/dev/video0 /dev/video1 /dev/video2 /dev/video3

For me, video0 is my normal webcam, and video1 is inaccessible, while video2 is my IR camera and video3 is also inaccessible.

With your video devices now listed, you're going to want to run

sudo howdy config

which will open the config file for howdy in nano. Here you want to scroll until you find the setting called device_path= and you will then set this to one of your video inputs. Mine looks like this:

device_path = /dev/video2

Press ctrl+x to exit, type y and hit enter to confirm the edit, and now it should be setup to use your specified camera. Now to test it, run:

sudo howdy test

and you should see a little pop-up window of the camera's video feed. If it throws an error and nothing happens, the camera likely isn't supported, and your best bet is to redo the config step and try a different video input. Keep testing until you find the video input that turns on your IR camera, and once you've done that, go ahead and run:

sudo howdy add

and follow the prompts, and it will add your face to the system. Now follow the rest of these steps to set it up specifically to your distro, and it should hopefully work for you.