With the TemperatureSetting trait.
When saying "increase temperature" or "decrease temperature" without specifying any number. We found that the default temperature adjustment seems to be 1.5 °C for our case.
This lead to the question Why it's 1.5°C? And does everyone experience the same behavior?
We tried reading the document but it dosen't contain information about this.
We also created issuetracker to request a feature for this.
You can try taking a look at the TemperatureRelative (https://developers.home.google.com/cloud-to-cloud/traits/temperaturesetting#action.devices.commands.temperaturerelative) attribute of the TemperatureSetting trait. This allows you to adjust the target temperature relative to the current state.
Based on what value the manufacturer puts here Google will decide by much to increase/decrease the temperature.