To reset the Thermo to factory settings, you will need to disassociate it first and then complete the reset on the device itself. Please follow these steps: 

Dissociate the Thermo:

1. Open the Withings app.
2. Select the Devices icon on the top right-hand side of the app to access the Devices menu.
3. Select All Settings.
4. Select Dissociate this device and confirm.
5. Go to the Bluetooth settings of your mobile device and locate the Thermo in the list of devices.
6. Select the icon to the right of the Thermo and select the option to 'Forget' or 'Remove' the device.

Complete the reset on the device:

1. Press and hold the button on the Thermo until the word 'SETUP' appears on its display (this may take up to 10 seconds).
2. Quickly press the button on the Thermo 6 times until the words 'FACTORY RESET' begin to scroll on the Thermo's display.
3. Quickly press the button on the Thermo 5 times and the Thermo's display will power off.
4. The Thermo is now ready to be set up again.