Performing these steps resets all system settings (e.g. ringtones, sound settings, display settings, etc.) back to their default values. Personal data, such as downloaded apps and media (pictures, videos, music), aren't affected.
From a Home screen, swipe to access all apps.
Navigate: Settings > System .
Tap Reset options.
Tap Reset Wi-Fi, mobile & Bluetooth.
Tap RESET SETTINGS.
If applicable, enter the PIN, password or pattern.