All Airport bases, like other routers, have the particularity of password-protecting the network settings and connection details so that nobody can modify them without going through this process first, but what happens if we forget the password?
In general, what we would do being the most direct way would be to start trying different passwords and after a few unsuccessful attempts, go to physically reset the Airport to reconfigure it with the usual waste of time to leave it as it was.
This no longer has to be the case due to the keychain service that OS X has and from which we can look at the assigned password As long as we know, yes, our system administrator password, a password much more complicated to forget because it is used much more for almost any action that minimally modifies any system option.
To do this, the first step would be to access the folder Utilities> Keychain Access. Once we are within the keychain access, we will look for the password that we are looking for, both for the network disk that we have connected to the Airport Extreme for example as if it is a Time Capsule base or simply the general password. In any case we will see that on the left side it is marked Keychains> Login and below in categories we will leave it in Passwords, in this way we will look in the Class for something like Station password or Airport disk password.
When we have located the entry as shown in the image, we just have to double click to open it and go to Show password field where we will then be asked for the administrator password so that when we enter it it will appear.
More information - Keychain Access, the great unknown