nvflash

 NVIDIA Video BIOS Update Utility. Suitable for most video cards that use PCB reference design and some brand-name video cards. The DOS version only works from "pure" DOS, in the absence of extended memory managers such as HIMEM/EMM386/QEMM.

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This is the official program from Nvidia for flashing the BIOS of video cards. Works from under the DOS environment.
Create a bootable floppy disk with DOS or a CD-RW with a DOS image, write the program and the new BIOS in the same place.
After booting into the command line, type:
nvflash <BIOS filename>
And follow the instructions that appear.

For persuasiveness and so that there are no unnecessary questions, I type:
nvflash -4 -5 -6 <Bios filename>

What to do if the video card does not boot after flashing?
1. Don't panic. The problem is easily solved.
2. There are two ways out: insert a second video card, for example, PCI and boot from it to flash a non-working video card with an old biosome pre-recorded on disk. Or work "blindly". Often the system is loaded, and if you, after loading the operating system, write in the blind:
nvflash -4 -5 -6 <old BIOS file name>
and press "Enter" you will return everything to normal without any problems.

For flashing BIOSes, there are programs for Windows as well. They come with Leadtek video cards, for example. But working through them is more dangerous and, of course, more convenient.