Question can't change drive letter to D

[Austinwftw]

So I updated my bios and for some reason it changed my drive letters which is affecting the programs I have installed so I went into windows disk management and changed all of them back but one as the letter D is not available as if it is still in use which it isn't if anyone has any ideas on things I could try it would be appreciated.
(edit my disk drive was set as D drive which did not appear on the top volume portion of disk management instead I had to scroll down from that page right click my disk drive and then I had to change it to another letter to have D back)

 

[USAFRet]

Please show us a screencap of the current Disk Management window.