How to Recover Unallocated part Space on USB Flash Drive?

Recovering  Unallocated Part Space on USB Flash Drive

C:\WINDOWS\system32>diskpart 

DISKPART> list disk
  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          465 GB      0 B        *
  Disk 1    Online          894 GB      0 B
  Disk 2    Online         3750 MB      0 B 

DISKPART> select disk 2                 //depends on disk
Disk 2 is now the selected disk. 

DISKPART> clean
DiskPart succeeded in cleaning the disk.

Run CMD Line Terminal on windows as Administrator 

Now try allocating Disk by going to computer -> (right click)Manage -> Disk Management ->
Allocate drive