Adding custom notification sounds is a great way to customise your phone more closely to your preferences.
Youll need to tap the Internal Storage option.
Options will appear at the bottom select Copy.
Copy here
Once youve copied the file, navigate to the folder Notifications in Internal Storage.
Copy your file there.
Copied file
When youve done so, open your options app.
Tap the Sounds and Vibration option, and then the Notification sound option.
So, if prompted, snag the one you want to set a notification sound for.