Windows 10: No option to Eject External HARD DRIVE (NOT USB Stick)

1. Click Windows icon in task bar.  Click on Run…
2. Type:

   RunDll32.exe shell32.dll,Control_RunDLL hotplug.dll

3. Press the Enter key or click on “OK”.
4. In the “Safely Remove Hardware” dialog click on the device you want to remove, and press Stop.

(from answers.microsoft.com)