First we need to goto the Settings app
The quickest way to access the phone’s general Settings is to swipe down the drop-down menu from the top of your device screen. For Android 4.0 and up, simply pull down the Notifications Bar from the top and then tap the Settings icon.
When the notification menu drops down, go ahead and tap on the Cogwheel in the top right of the screen.
Once in the Settings Menu scroll down till you see one of the following and select it
Sounds and notifications
Select Do not disturb
On the next screen, confirm Turn on now is unchecked or any toggle switch related to Use Do not disturb