Take a M3x60 SHCS screw [HD-BT0203] and place a M3 flat washer [HD-WA0038] then a dual v3 fan Spacer [PP-GP0501] on the screw, then insert the screw in one of the top holes in the heatsink, as shown. Repeat for the other top hole.
Once screws are fastened flip the extruder head over and check if screws protrude the mounting plate, if so then loosen the screws till they are at least flush the mounting plate, as shown.
Take the two M3x35 SHCS screws [HD-BT0043] and place them through the two bottom holes on the heatsink fan, once they are through the fan you can slide a M3 flat washer [HD-WA0038] then a M3x5 Spacer [HD-MS0555] followed by one more M3 flat washer [HD-WA0038] on the screw, as shown. Repeat for the other screw.
Fasten the fan to the heatsink, as shown.
Make sure screws are firmly holding the fan and heatsink in place, but do not over tighten the screws