How to install custom firmware

[dsiegfried]

I purchased my N2 from someone who had loaded custom firmware to run a Berd-Air fan off the HE2 pin.
I had to replace the board and after I updated the firmware now the Berd-Air isn't working.

I found the settings I need to change in pins_RUMBA.h but I need advice on the basic steps of compiling and uploading the firmware.
I have used Arduino before to compile and upload firmware to another printer but never with a Raise3D and I don't want to risk bricking it!

Could someone please walk me through the basic steps like what files are needed, how to integrate the pins_RUMBA.h file, how to physically connect to the board, etc?
Thanks