How to use multiple cameras?

G-d willing

I am completely new to Open.HD and quite excited to start with it. Yesterday I bought my 2 raspberry PI 4B with the WiFi adapters by ASUS. So I plan on hooking up as soon as possible.
My question is regarding the cameras.
Since my rig has 3 cameras (2 USBs and one of them is the Hawkeye Firefly Split 4K which connects through a micro HDMI port), how can I work and switch between them? I understood (I already read other posts on the forum) that it is possible to use more than 1 camera, but I didn’t understand how.
Can you please refer me to the proper documentation about it? Any kind of tutorial will be helpful.

Thank you.