Assign a Drive Letter Permanently to a Flash Drive
You can force your Windows operating system to always assign the same drive letter to a flash drive.
Go to Administrative Tools in the Control Panel. Then Click on Computer Management.
In Computer Management, you'll see a list of all of the drives connected to your computer. If you right click on a drive you'll have the option to change the drive letter.
Clicking 'Change' . . .
. . . will give you the option to assign a drive letter.
Anytime in the future when the drive is plugged into your PC, it will be assigned the chosen letter.