How about DiskPart in a CMD prompt?
DiskPart to assign drive letters via Command Prompt
If you ever need to set a drive letter via Command Prompt, you can use diskpart.
1. Open a command prompt
2. Type in diskpart
3. Type list disk to see a list of disks
4. Type select disk # (where # is the disk you want)
5. Type detail disk to see partitions
6. Type select volume # (where # is the volume you want)
7. Type assign letter=x (where x is the drive letter)