Before the reset, remove the battery from the door push for about 10 minutes, press the push a couple times to remove the residual voltage and put back the battery to start the reset. 

To reset it, press the 'L' button on the front of the chime for 10 seconds: 

After the reset please try to pair them again, make sure after plugging the chime back into the socket (unplug it before pairing again) that you immediately press the bell push to pair it to the chime: