If you have one of these, and bought it in the US, it probably reads out in Fahrenheit. If you want it to read out in Celsius instead, ignore all the results you found on Google that didn’t work, and just do this:
Open the battery door, and remove one or both of the batteries, look for the switch I’ve highlighted, and switch it from F to C. Reinstall the batteries, and the door, and move on with life… Your thermometer will still give you red-yellow-green warnings based on the proper scales for forehead temperature, but the readout will now be in Celsius.
You’re welcome. 🙂