Start here: [SALE] FW3A lighted TIR board multicolored with LVP, stabilized or High/low
The flashing process is pretty much the same as any other attiny85 based driver. Lexel has a bit of info and a precompiled .hex file in his thread where he is selling these boards.
You’ll need a USBasp, an SOIC8 clip and something to connect them (dupont wires are the usual recommendation). For instructions, there is a thread going up for the D4V2 and the instructions will be adaptable to the FW3A. The main differences between the lights are the method of connection (FW3A uses a generic clip and the D4V2 uses a special programming key), the chip being flashed (attiny85 instead of attiny1634), and the file to be flashed.
I think there is an old thread/post by Hoop on how to flash attiny based drivers as well. (they are all very similar)