I've made a terrible mistake

Recovering my much loved but seldom used V2 from storage, I fired up an instance of Octoprint that warned me that the firmware has a fire risk.
I thought, oh - cool, it's been quite a few yers since I've used this machine, maybe there's a firmware update.
I downloaded the instructions and follow along till I erase the EEPROM, then go to build the firmware to get errors.
Long story short, you need an ancient machine to run the version of Arduino IDE required to compile the firmware, which I no longer have access to, and I've now erased the existing firmware so my machine is like a brick.
Can anyone help with the configuration file for Marlin, so I can flash that on, or a way for me to recompile the original firmware? I'd be forever greatful if I can revive this machine and get it printing again!!!
