Run diskpart command line by press Windows + R to open Run box, and type diskpart, press enter; and input the following commands to assign drive letter:
Launch the Macrorit Disk Partition Expert, you'll see all detail information of the partition and disk.
Right-click the volume whose drive letter you want to change, and then click Change Drive Letter.
Select a new drive letter from the list of available ones. To leave the volume without a drive letter, click Do not assign a letter.