Looking to reset your Apple Airport Extreme to the default settings?

Here’s the steps:

Factory default reset

1. Disconnect the base station from its power source.
2. Press and hold the reset button with a straightened paperclip, then plug the base station back in while continuing to hold the button for approximately 5 seconds until you see the three status lights glow.
3. Release the button. The base station will factory default reset.

More details here.