Installed RatOS but can't flash the Octopus

Hello guys. I'm building a Ratrig V-core 3.1 (500mm) and I've flased my raspberry Pi with RatOS. I can't find a way to flash firmware on my Octopus V1.1 board though because I know how to do it and after reading a lot of stuff regarding this online, I'm still stuck at the same point. Any help with this is greatly appreciated. Thanks