How to use the multifunction button in M23?

In Player mode: Add to Favorites (default option), Play next song randomly (randomly play the next song according to random play rules), Play/Pause, Delete currently playing song, Switch filter (cyclically), Switch equalizer (cyclically), Enter USB DAC Mode, Enter Bluetooth Receiving Mode, Lock screen/Wake up, No function

In Bluetooth Receiving mode/USB DAC mode, the multifunction button is forcibly set to: No Function.

Note: This button only responds in Android mode/Pure Music mode, and some functions only apply to FIIO Music.