DIAGNOSIS The night light has its own dedicated button. If pressing it isn't working, the control might be stuck or the unit may need a reset.
FIX First, try a firm, deliberate press on the crescent-moon-shaped Night Light button. You should feel a tactile click. The light should cycle: Bright > Dim > Off.
IF THAT DIDN'T WORK Unplug the purifier from the wall for 60 seconds. This performs a hard reset of the control board. Plug it back in and try the night light button immediately.
HEADS UP In Auto Mode, the display dims but the night light stays on your last manual setting. You must manually turn the night light off if you don't want it.