Press and hold the measurement button.
- When the device is off, press and hold the measurement button for 8 seconds to enter unit switching mode. Under this mode, both Fahrenheit and Celsius should flash at the same time.
- Press the measurement button to switch to Fahrenheit or Celsius. The corresponding symbol of the selected unit after switching will flash.
- After selecting the unit, press and hold the measurement button for 8 seconds to leave the unit switching mode.
Source: iHealth Labs