You can specify a custom sound, that iOS will play when it receives a local or remote notification for your app. For more details, you can consult Apple's documentation.
Remember that the default sound is played when:
To add the sound file to your project, you can simply drag and drop it to your resource folder. Make sure you check the box Copy items if needed.
In the Accengage dashboard, you can easily specify this sound when composing a push message by selecting "custom" in the sound section, and enter the file name with its extension (customsound.wav for instance).
Prefer a short file name.