The "Change Water Panel" light is merely a timer, it does not know if water panel replacement is needed.
To reset the light:
1. turn knob all the way to the right toward 'Test/Reset'
2. leave the knob there a few seconds and then turn it back to the setting of your choosing.
Proper setting depends on your home.
Low humidity? You could try the '7' setting, but lower if your windows sweat.
Unfortunately, in the winter, ideal humidity level is often unattainable due to the way our homes are built. Not enough air moves across the inside of our windows, so windows get cold and sweat...like a glass of ice water in the summer.
Late winter often brings low indoor humidity.
Slightly warmer days + persistent, dry northern air = The humidifier can only run when the furnace runs. "Warmer" days call for less furnace operation, which means less humidifier operation, yet the dry air persists.