Administrator account lost

Try using the steps in this article:

Change or reset the password of a macOS user account - Apple Support

Good luck!

To see the user name, in the standard account, go to System Preferences/Users & Groups, and the user name for each account should show in the left panel.

User Password Reset.   

User Password Reset (2).         

jesslynturn Said:

"Administrator account lost I can not access the admin account. I do not know the user name or password. How to do reset both with only a standard account available?"

-------

Consider the Following:

A. Is this a Used Device?:

If this is a used device, then contact the seller, asking for the password. Also, have them sign out of iCloud.

B. Locate an Administrator User Name:

1. Boot: in to Safe Mode (hold down command + R upon boot
2. Enter: password (if applicable). You might not be able to get past this part, if a password does not work.
3. Go to: Utilities menu (top of screen)
4. Select: Terminal
5. Enter: this command and then press return key

dscl . -read /Groups/admin GroupMembership