How to probe my smart thermostat for reprogramming?

I got a Greenlite AIRZ thermostat which connects to my home wifi so that I can change the settings remotely on my phone. The app is, however, difficult to use, so I’m thinking about making my own. I found its IP address, put it in a browser, and it said verbatim File / not_found. The thermostat also rejects my request to connect to port 21/22. How should I proceed from here? Is the underscore between not and found a quirk of a specific server that would allow me to probe further?