To change AirPods settings, you need to go to Settings > Bluetooth and pick your AirPods from the list.
However, your AirPods need to be connected to your device. That means the lid needs to be up or the 'pods need to be in your ears.
Once they're paired, tap on the blue "I" icon on the right side. That will bring you to a menu from which you can change the double-tap behavior.
I prefer to have the right AirPod pause the song when I double tap, and have the right AirPod go to the next track.
You can also rename your AirPods, and specify whether the left or right AirPod has its microphone on when you're making calls.
