DIAGNOSIS: That light isn't triggered by a sensor; it's a simple timer. It comes on after a set number of cycles (usually around 30-40) as a reminder, regardless of how clean the filter actually is.
FIX: To reset it, make sure the filter is fully seated in its slot. Then, with the dryer door closed and the machine off, press and hold the END OF CYCLE SIGNAL button for 3 seconds. You should see the Clean Filter light blink and then turn off. If that specific button doesn't work, try the WRINKLE SHIELD or START button—the reset method can vary slightly.
IF THAT DIDN'T WORK: Try unplugging the dryer from the wall for 5 minutes. This can sometimes reset the reminder timer. Plug it back in and see if the light is off.
HEADS UP: Don't ignore the reminder just because you can reset it. The filter and the lint trap cavity do need regular cleaning for performance and safety, even if the light is annoying.