There is no uninstaller for a portable version. You just delete it.
If you had nothing else on that drive, then open the drive, create a folder named NVDA, then select all else on the drive and move it to that folder.
If you want the drive space available again then just delete the files on it or format it again.
Brian - Windows 10 Pro, 64-Bit, Version 1903, Build 18362
The color of truth is grey.
~ André Gide