I want to reset my iPad Air and I didn't remember my restriction code how can I recover it

The only way to recover it is to remember it. If you can't then try recovery mode and your computer's iTunes to reset the iPad back to factory defaults (you've copied off anything that you want to keep, photos, purchases, documents ?), there are instructions halfway down this page : If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support.

Hi

The code you need is just your PASSCODE

You use this each day when you turn your ipad on.

Cheers

Brian