The tool requires exclusive access to the drive. Close all antivirus software (they may flag the tool as a hacktool—which it technically is).
Run Wndmifit.exe as Administrator. The GUI is usually spartan: a dropdown for drive selection and a few checkboxes. wndmifit tool
But approach with respect. Read the controller datasheet. Verify the firmware checksum. And always, always have a backup of your data elsewhere. The tool requires exclusive access to the drive