Music Speed Changer allows you to import audio files from your device and cloud storage.
To get started, go to Files, which is the fourth main tab in the app main menu and tap on Import at the top of the files section to get started.
The app will open your device's file browser to give you access to your local files and available cloud services.
To open local files to tap "On my iPhone" and browse to the tracks you wish to import. Select the tracks you want to import. Tap Open. The files will import and show up under files in the app.