Play background sounds on AirPods
When you use supported AirPods with iPhone or iPad, you can play calming background sounds—such as ocean or rain—to mask unwanted environmental noise and help minimize distractions so you can focus or rest.
Wear your AirPods, and make sure they’re connected to your device.
On your device, go to Settings
> Accessibility > Audio/Visual > Background Sounds, then turn on Background Sounds.Set any of the following:
Sound: Choose a sound; the audio file downloads to your device.
Volume: Drag the slider.
Use When Media is Playing: Adjust the volume of the background sound when your device is playing music or other media.
To quickly adjust the volume and turn background sounds on or off, add Hearing 
to Control Center. See Use and Customize Control Center in the iPhone User Guide.