If you already changed the Wifi SSID and password, your only option is to go through the setup for each camera. DO NOT delete the cameras first. The system will realize that it is an existing camera and all your setting will be preserved.
I also don’t have a Thermostat, so I can’t speak to that device, but occasionally I have to reconnect a Cam to Wi-Fi (because I’m trying to use a different SSID or because it’s having connectivity issues), and what I usually do is just press the SETUP button once (not a press-hold, because I’m not trying to factory reset it) and then do the normal device add procedure in the app up to the point where it asks me to name the Cam. Then I just abort by swipe-closing the app. When I re-launch the app, the Cam is there in my devices with the name I had previously assigned it, and the settings are intact.