Reformatting a Drive

Unmount the drive

Reformat The Drive

That should bring up a dire-sounding warning that you are about to delete everything on the drive. That’s unavoidable when reformatting, so make sure there isn’t anything you want on there!

If that doesn’t do it, I’m not sure what else to suggest other than bringing the drive back. You can probably order a Mac-formatted one from Amazon.com.