Airstep is one of the unique moves that Sora has in Kingdom Hearts 3 that allows you to reach platforms and areas that you otherwise couldn’t by using the shotlock reticle. There are a couple of different ways to Airstep in Kingdom Hearts 3 but you’re going to need to use the Shotlock to target an area to begin with.
To bring up the Shotlock reticle you will need to press the RB/R1 Button the controller. This will open up a small circle on the screen. As you move the circle around you will see areas that you can use to lock on to and move forward. Simply highlight these blocks with the shotlock and the press the X/Square button to move with Airstep.
While other shotlock functionality requires that you have focus, Airstepping does not. You can Airstep as much as you like without worrying about having Focus.
There are also some other uses for the Airstep. One such use is on enemies. If you find yourself in an area where you feel like an enemy is too far away from you, you can use Airstep to reach them. Simply use the Shotlock on an enemy like you would the environment and press the X/Square button and you will essentially warp to them, treating them like a platform of sorts. You can then begin attacking them as you get closer.