It outlines the steps to transmit the time sync audio beeps with headphones to the watch which after a few minutes results with the watch being synced as if the watch owner was actually in Japan.

Place headphone speakers by the atomic radio clock’s internal
antenna with the volume as high as possible before it starts to
distort. Or place the clock’s internal radio antenna as close as
possible to the smartphone speaker. Again with the volume as
high as possible before it starts to distort. When time sync
receive mode is active the clock will sync within 2 to 3
minutes.