Seven pinned threads, and the answer to the question that comes up over and again isn't one of them.
You'll need a separate pc, a wired usb keyboard, a usb stick, a link to the Atari firmware, and a program to write the firmware to that USB stick. If using a Windows PC, copy and paste rufus.ie into your web browser. That's a good/free program to write the firmware.
A link to the firmware (it's a google drive link) can be obtained via a pinned message in the Atari VCS discord.
Easy to follow instructions for the process can be found here if you search (sorry, I don't have the exact thread handy.)
I just fixed this on a new machine this morning, but I remembered how to do it because I had to do it with my old machine when I got it.