Make sure that the sound button is not muted.
In case you are still having issues after that, please select your device and follow the steps below:
Windows devices:
You can adjust your system volume using the sound icon placed bottom right in the system tray.
Mac devices:
You can adjust your sound settings by following these steps:
Open "System Preferences"
Select "Sound"
Adjust your "Output Volume"
Android devices: https://www.dummies.com/consumer-electronics/smartphones/droid/how-to-adjust-your-android-phones-volume-and-display-settings/
Open the Settings app
Choose Sound (on certain Samsung phones, the Sound option is found on the Settings app’s Device tab)
Set the phone’s ringer volume by touching Volumes or Volume
Drag the Ringtone slider left or right to specify how loud the phone should ring for an incoming call.
Touch OK to set the ringer volume.
iOS devices: http://www.spalding.org/faq/apple-ios-app-no-sound/586
Double tap the home button
Swipe from left to right
Tap the speaker icon, placed far left
It should show “Mute Off” below the Play button
Listen to app sound once again
Turning off the soft mute feature on the iPhone/iPad should fix the absence of sound.
If you have difficulties getting the speaker icon to show while swiping from left to right, you can also turn off the soft mute by following these steps: Go to Settings / General / "Use Side Switch to":
Select "Mute", then use the rocker switch on the side to turn on the sound.
Plus make sure that your mute button on the upper left side of your phone is set to muted (in other words, it's set to red).