If an app is using a disk you want to eject from Mac
You may not be able to eject a disk if one or more apps are using it. In some cases, a warning message may identify the app that is using the disk. You can also hold down the Command key and press Tab to see which apps are open and switch to a different app.
Quit the apps that are using the disk, then try to eject it again.
If you can’t quit an app, close the documents that are on the disk you want to eject, then try to eject the disk again.