There's a couple of easy methods to rename your flash drive.
First, is to click on the drive name, and just type the new name. I usually just hit "tab" when finished, but you probably don't have to do that.
Another, is to click on the drive icon, then press Enter. You should see the name highlight, and just type the new name - which will replace the existing name.
Another, is to select your flash drive, then right click on the drive, choosing Get Info from the contextual menu.
Click on the triangle next to "Name & Extension". You'll see the name block appear, so double-click on the name, and type the new name.
Press Tab, or Enter to accept the new name.
I do get a "-43" error every time, but the name still changes each time I try. I ignore that -43 error that I get.
There's probably a number of other methods that can rename drives, such as through the terminal, but I don't use others (or haven't used for years).
If you still can't change the name, you should probably also make sure that you can copy files TO your flash drive. That will quickly tell you that the flash drive is writeable.