Right-click the ribbon that's showing as "Raw" in Disk Management and choose "Change Drive Letter and Paths".
Click "Add"
Choose a drive letter and click 'OK'.
Wait a few seconds for the ribbon to update.
When you have important data you should not rely on just one drive to save it on.
You should save it on at least two hard drives so that you have a backup.
All hard drives fail eventually -- remember that and buy another external hard drive for storage of the same data that's already on your Toshiba drive.