how to eject seagate backup plus from MacBook Air

Hi there gerbil48,

From what we can tell, you're unable to eject your external Seagate drive by dragging the icon to the Trash on your Mac. We're glad you've joined us in Apple Support Communities, and we can provide some guidance. 

"If you can’t eject a storage device, another app or user may be using one or more files on the storage device. See If an app is using a disk you want to eject and If another user is using a disk you want to eject." Have a look at this link to learn more:

Use external storage devices with Mac

If that doesn't seem to help, follow the steps in this link:

If you can’t eject a disk from Mac

Cheers!

Follow directions from @ Sparks0829 - If not successful - Right Click icon representing the Seagate drive on Desktop and menu will appear and choose Eject.