macOS Sierra: If you’re asked for an administrator name and password
To complete certain tasks, you must enter the name and password of an administrator to verify that you are a user with administrator privileges. If you’re in a secure environment where smart cards are required, you must insert your card and enter a personal identification number (PIN) instead of a password. Be sure you know which app is requesting this information.
If you don’t know an administrator name and password, ask the person who set up your Mac for help.
If you set up the original user account but don’t remember the password, see If you forget your login password.