Go to settings > sound and drag the slider to the maximum volume.
If the horn rings, please follow the following steps. If there is still no sound from the speakers, please contact Apple technical support.
If your device has a ringtone/mute switch, make sure it is set to the ringtone position. (If you see the yellow label, the device is muted) Restart the device.
Open an App that can make sounds. Use the volume button to adjust the volume or move the slider in the control center.
Go to Settings > Bluetooth and turn off the Bluetooth function. Then check the sound again.
Connect headphones. If you can't hear the sound through the headphones, unplug the headphones and clean the dust or impurities in the headphone port of the equipment.
If your equipment is installed in a protective case, please make sure that the protective case does not block the speaker.
Use a soft brush to clean the impurities in the horn and lightning interface.
Upgrade to the latest version of iOS system.