1. Place both earbuds back in the charging case, wait for 5s, then take them both out and try again.
2. If this doesn't work, then reset the headphones refer to the manual and re-pair:

    (1) Place the earbuds into the charging case and make sure they are being charged for at least 10 seconds.
    (2) Keep the charging case open and press and hold the button on the charging case for 10s until the LED indicators flash red 3 times.
    (3.)Then wait for 4S and the LED come into white light flash quickly. You could connect your iPhone this time.