Until iOS 11, you could only choose between activating Siri, or Play/Pause media when double-tapping either the left or right AirPod. But with the release of iOS 11, Apple gave AirPods users a few more options as to what a double-tap gesture can do. Indeed, we have a couple more controls available, and we can also choose specific controls for both the left and right AirPod.
How to customize your AirPods shortcuts