He’s referring to the last 4 photos in my comment here [Official] HP 290-p0043w Owner's Thread - #631 by cobalt
There’s 2 spring loaded clips that hold the heatsink down. You can pop them out by gently squeezing the tip that’s poking through the circuit board. I used m3 nylon screws washers and lock nuts to attach the fan to the heatsink and circuit board. If yo want to go through the entire height of the fan, heatsink and circuit board the m3 screws need to be something like 3 inches below the screw head. I got 2 inch screws and managed to get them through just the bottom holes of the fan and the rest since nylon is plastic. They bend just enough to make it work