I'm stuck trying to fix my CR10S-S4

When trying to update the firmware for my printer, I accidentally followed the instructions for a V1.X board instead of for a V2.X board and now my screen is blank on boot.
When trying to flash firmware through USB through Arduino or VSCode, it appears as unresponsive.

I apparently need to get a new bootloader, but I don't have an Arduino Uno or anything except for this USB ISP thing that came with the BL Touch I bought (the whole reason I need new firmware).
Is there anyway I can put a new bootloader on this board with this, or should I just replace the mainboard all together?