Press the reset for 1sec to reset the password.. and change it for everything.. I am not sure you can recover it and I am not even sure what password.. there are three sets of passwords in the TC at least.
You could even have a pppoe password.
Which have you lost?
Read up how to recover using soft reset.
If you have the computer that was used to setup the airport you might be able to recover the password from the keychain.