Locate the purple smart button on the back of your Liftmaster garage door opener. The smart button may be behind a light cover and its always near the antenna wire.
Step 1:Push the purple smart button and let off.
Step 2:Hold your remote button down until you see the light bulbs flash on and off or you hear a clicking sound.
Now try your Liftmaster 371LM remote and it should activate your Liftmaster garage door opener.