Turn your Drop Scale upside-down. Use a coin to open and remove the battery compartment door. Insert the battery into its housing, with the text on the battery facing up (see diagram below). Once you are happy that the battery is in place correctly, replace and close the battery compartment door using the coin again.
Turn your Drop Scale back over, and tap the button on the front of your scale. The LED light will pulse briefly when the battery is installed correctly.
If you are having trouble getting the LED light to pulse, please make sure that the battery you just inserted is in fact a CR2477 and not a CR2477N. The latter is, despite the name similarity, a different battery and will not work with Drop Scale.