There are no admin accounts on your Mac. All the users are standard users.
- Hold cmd + S when turning the Mac on to boot into Single User Mode.
- 2. Type mount -uw / and press Enter.
- 3. Type rm /var/db/.applesetupdone and press Enter.
- 4. type reboot and press Enter.
This will restart the machine and you will be prompted withe the setup assistance screen as if you had just used the computer for the first time.
When creating an account in the setup do not choose a username that is already on the machine.