Erase and restore your base station or Time Capsule using AirPort Utility on Mac
Before you give away your base station or Time Capsule, erase and restore it to Apple factory settings. If you have a Time Capsule, you should also erase your data from the Time Capsule disk.
Open the AirPort Utility app
on your Mac, located in the Utilities folder in the Applications folder. In the graphical overview, select the base station you want to reset, then click Edit. You may need to enter a password for the base station.
If you have a Time Capsule, follow the steps in Erase an AirPort Time Capsule.
To erase and restore the base station to Apple factory settings, choose Base Station > Restore Default Settings. Read the message, then click Continue.