If one ear bud is working and one is not they are not pairing correctly. Please turn off the working ear bud by holding down the button for about 5 seconds until it turns off. It will also talk to you so if it's in your ear its helpful "power on-power off". Next put it inside the provided ear bud case.
Take out the non-working ear bud and turn it on and try to pair it with your phone individually. Sometimes it's helpful to turn off your Bluetooth on your device first and turn it back on. Turning off the ear buds resets them.