Unfortunately, the short answer is: you can't. Autoplay doesn't work on mobile browsers.
Mobile Safari (the default browser on iPads and iPhones) and other mobile browsers (Chrome, etc.) do not allow audio files to start playing automatically when a page loads. Instead, they require a person to initiate an audio or video file via interaction with the device, which doesn't help in this case (if you're interacting with the page, then you already know that a new order needs to be confirmed!).
If you're curious, you can read more here:
If you feel that it's important to have an audio alarm when new orders come in, then we would suggest purchasing a small, inexpensive, Windows laptop, which you can find on any of these websites:
Windows laptops tend to be the cheapest, and they allow for multiple browser types to be downloaded, which can be very helpful.