If you know how to use it, it came with MS-DOS. Hexedit (pre-95) or Debug allow you to do almost anything to a floppy, includes telling the floppy it is a 20G floppy!
If you're asking for technical help, please be sure to include all your system info, including operating system, model number, and any other specifics related to the problem. Also please exercise your best judgment when posting in the forums--revealing personal information such as your e-mail address, telephone number, and address is not recommended.
Floppy Disk Repair utility