Try these steps:
1. Open Command Prompt. (CMD)
2. Type: diskpart
3. At the DISKPART prompt, type: list volume
Make note of the number of the simple volume whose drive letter you want to assign, change, or remove.
4. At the DISKPART prompt, type: select volume n
Select the volume, where n is the volume's number, whose drive letter you want to assign, change, or remove.
5. At the DISKPART prompt, type one of the following: assign letter=L
Where L is the drive letter you want to assign or change.
You can make L any letter as long as it is not already assigned to a drive.