Microsoft DiskPart version 6.2.9200
Copyright (C) 1999-2012 Microsoft Corporation.
On computer: COMPUTER
DISKPART> list disk
Disk ### Status Size Free Dyn Gpt
——– ————- ——- ——- — —
Disk 0 Online 298 GB 0 B
Disk 1 Online 7509 MB 6619 MB
DISKPART> select disk 1
Disk 1 is now the selected disk.
DISKPART> clean
DiskPart succeeded in cleaning the disk.
DISKPART> create partition primary
DiskPart succeeded in creating the specified partition.
DISKPART> exit
This info was copied from: http://geekswithblogs.net/ilich/archive/2013/04/26/recovering-unallocated-space-of-a-usb-flash-drive.aspx