1 - Turn the water off
2 - Cover the drain and avoid loosing parts.
3 - Remove the square handle round cover. It snaps off.
4 - Remove the screw and pull the square handle from the stem.
5 - Use the kit tool to remove the  recessed nut
6 - Pull the cartridge out, use pliers to hold the stem
7 - Remove the inner cup washer and spring (best to use a paper clip and bend the end like a small hook to fish them out
8 - Place the cup washer and spring at the end of a pencil and hold it in place while guiding it to the hole, remove the pencil while keeping the parts in place with one finger. With the pencil rubber end, push it down gently until cup washer is recessed in the hole or almost flush with the large hole flat surface.
9 - Insert the Cartridge downward until it slides in the valve grove and gently push it down
10 - Screw the Holding Nut by hand and tighten it with the tool
11 - Turn the water on and test it. If done correctly install the handle and enjoy the Jacuzzi.