Eject disk from MacBook external drive

Try holding down your trackpad button (or your left mouse button) and restart your Mac. Hold the button down until the desktop appears. This will trigger the system to eject your disc before OS X begins loading.

If the disk does not appear as a volume on the Desktop you can just unplug it. Is that the situation? If so, what indication do you have that it's not ejected?

Incidentally, if your laptop has the Touchbar I believe that the eject key appears at the right-hand end of that (I can't check this): but it does the same thing as Command-E and if there is nothing mounted on the Desktop there is nothing to select and eject.

Was the drive accessible in the Finder at any time after you plugged in the USB drive? If not, then it was probably never mounted and would be safe to just unplug the drive.

Do you have Finder configured to show the mounted external drive? In the Finder, click on File --> Preferences. On the first tab make sure mounted drives are selected so they will show up on the Desktop. If you click on the third tab I believe, it will show a long list of items which will appear in the Finder's side panel. Make sure to check the option for mounted or external drives. I'm not at a Mac at the moment so I'm not sure of the exact name of each option, but it should be easy to figure out.

try. https://support.apple.com/en-us/HT201295