Please check if the sound option is turned on.
You check the setting but you still cannot hear any sounds? Please exit the game and log in again.
If above steps didn't work, please try following steps:
1. Check if your device is on mute mode.
2. Plugged and unplugged your earphones.
3. Check if you can hear sounds from other applications. If you cannot hear any sounds from other application either, it might be problems of the device, not the applications.