Thanks, Borislav!
You guessed it right, this function only takes one argument tho, you should just pass the path of the firebase node to it. Probably Firebase.getInt(“CO2Limit”) according to your example.
Here's a link to the documentation in case you need more features: https://firebase-arduino.readthedocs.io/en/latest/#_CPPv2N15FirebaseArduino6getIntERK6String