1. Assemble the 2 brackets according the below picture.
2. Assemble the fan with the fan sticker side against the fins of the cooler. Use the springs for this.
3. It should now look like this.
4. Remove the protection plastic on both sides of the thermal pad and put the thermal pad on the cooler.
5. Use the screws, spacers and nuts to assemble them on the raspberry pi like in the picture below.
6. Go to THIS instruction for how to wire and setup the PWM fan for raspberry pi OS.
If you wonder how to Assemble this cooler into the KKSB Raspberry Pi 4 Case Tall, see THIS instruction.