Thank you, AlanMexicali. The form has probably changed since you used it. There was only the Pieza numero and the NUT. We decided to visit INM today, and they said that the password is emailed to you. This had not happened to us, but today I entered our Pieza numero (include the six zeros) on the above mentioned website and hit the button to recover a password. The password has just now been emailed to us. Thank you all for your assistance!
Joyce