Forgot Macbook USERNAME, can’t login

Shutdown the computer.

Start the computer, then press and hold down command and R keys to start into macOS Recovery.

When you see the Apple logo and the progress bar, release the keys.

You have to press hard the Trackpad to register the click.

Select the “Language”, if not already.

Click the arrow button at the bottom.

Wait until  OS X Utilities window shows up.

Move the mouse pointer to the menubar at the very top of the screen, click "Utilities” and then select "Terminal"

from the dropdown.

Terminal window will appear.

Type in   resetpassword   and press enter on the keyboard.

Reset Password window will open showing all user names.

Write it down.

Quit Terminal.

Quit all windows.

Choose "Restart" from the dialog or  menu.