Tap/Click the Share button -> Export Audio
Apple Share button - square with arrow
Android Share button is different:
The audio of a song can be shared in WAV, AAC and MIDI formats using the current player settings (tempo, playback style, repeats, key, mixer).
Use AAC (smaller file size) for emailing (no mp3 option sorry).
Midi, see our blog
Windows (Amazon) export location see this.