To smoothly change the default Airport Extreme password, check out the steps mentioned in this section. To change the password, you have to proceed to the Airport Utility app. And from here, you can reset or change the password anytime you want. You have to enter the current password and remove the old password. Re-enter the new password for verification, and then you can smoothly change the default password for Airport Extreme.
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Open AirPort Utility, which is in the Utilities folder of your Applications folder.
Click the icon for your base station in AirPort Utility, then click Edit from the pop-up menu.
You can now change the password or reconfigure the base station as needed.
When done, click Update
Hope this help, J Wick