Open the settings on your smartphone or tablet.
Go to the "Sound" section.
Click on Default Notification Sound.
If you want to change the sound to any of the standard ones, click "Media Storage" and select the one you like.
You can find the right sound for your phone on the Notification Sounds website. I advise you happy birthday instrumental download and you will see for yourself how good this site is
And to turn on the notification sounds you have to ..
Open your phone settings.
Tap Apps & notifications Notifications.
In the "Recently posted" section, click on the app.
Select a notification type.
Adjust the settings as needed. Select Alerts or Silent.