How can I extract audio files from an app?
Use Apple Configurator 2 to update the app on your iOS device, but before disconnecting the iOS device, copy the iOS app out of the Configurator's temporary directory.  See: 

How do I download an iOS App (IPA) file to my Mac after iTunes 12.7 update?

for how to find this directory.  If the media assets of an app are not encrypted or obfuscated, you can sometimes find them by unzipping the .ipa file.