Flip board over. Ensure fin slot is free of debris.
Remove fin screw and metal bracket from fin then re-attach bracket to the tip of the screw as in the picture.
Holding the screw, insert the square bracket into the square hole in the center of the fin slot. Next, slide it towards the front of the board.
Insert the rear base of the fin into the fin slot through the square hole.
Slide the base of the fin towards the rear of the board.
Bring the front of the fin down so that the hole in the front lines up with the metal bracket.
Insert the screw and hand tighten until firmly in place.
(If you have a screw that requires a screw-driver, do not over tighten)
All done! Remember to remove the metal bracket when you disassemble the board later.