When you first unbox your Corentium Home 2, the default units are those customarily used in the USA; Picocuries per liter (pCi/L) for radon and Fahrenheit (°F) for temperature.
There are two ways to update the units if these are not what you prefer.
When you link your Corentium Home 2 with your Airthings app account, the device will automatically apply your preferred units as defined in your User Settings. The units you define in the User Settings are applied to all devices you have in your Airthings app account.
If you are using Corentium Home 2 without the Airthings app, you can do this on the device itself. Remove the back cover and press the Units button while looking at the device display. Different combinations of radon and temperature units will appear so just stop pressing when you have the combination you want.