How to turn on the background music automatically?

It is not possible to play the music automatically, unfortunately. 

Browsers (Chrome, Firefox, Safari, etc) have strict policies on audio auto-playing, which our app cannot override.

The usage policy of the browsers is designed to improve user experience by granting the user complete control of the events on the page, and thus avoiding being disturbed by a sound that the user has not requested.

This is the reason for the "play/mute" button that our app displays at the bottom left corner of the screen. Your customers will be able to play the sound by clicking on that button.