If you forget your AirPort base station, Time Capsule or Wi-Fi password
If you know the password for your AirPort base station or Time Capsule, but don’t have your Wi-Fi password, you can see a list of your passwords and shared keys. You can also manually reset your base station and create a new base station and Wi-Fi password during the base station set-up process.
View your passwords
Open the AirPort Utility app
on your Mac, then select the base station in the graphical overview.Click Edit, then choose Base Station > Show Passwords.
Reset your base station
While the base station is plugged in, use the tip of a ballpoint pen to press and hold the reset button
for no more than 5 seconds.To connect to the wireless network, click the Wi-Fi icon
in the menu bar on your Mac, then choose the network. (Because you just reset the base station, no password is required.) Open the AirPort Utility app
on your Mac, then select the base station in the graphical overview.Select the base station, enter a new password for the base station, then click Update.
Important: If you don’t make any changes within five minutes after resetting your base station password, you must reset the base station again.
To set a new wireless password, follow the steps in Change your Wi-Fi network’s name, password and security settings.
See the Apple Support article How to reset your AirPort base station.