Hi , the tweak is really simply ...
On the plug 4 wire on the fan (black / red / blue / yellow) ... unplug ONLY the blue wire , and connect this on GND on miner (directely on psu or black wire on fan) and interpose a potentiometer (between black and blue wire) for adjuste speed

I want to do this tweek on my miner too. Can you post a photo or a diagram for how to connect the potentiometer?