This may not be the right place to get help... But at the GitHub MarlinFirmware forum, there are experts that can get a boot loader onto any AVR board.
I've never needed to do that. But if I kill the boot loader, I'm confident somebody there will have both what I need and the instructions to fix the board.
I don't think you need to worry about killing the board.
I've never needed to do that. But if I kill the boot loader, I'm confident somebody there will have both what I need and the instructions to fix the board.
I don't think you need to worry about killing the board.