The installation of this is fairly straight forward but you'll need to use slightly longer screws than the ones that are currently attaching your light switch cover. 6-32 x 1 inch machine screws with a round head should work fine. 

1. Slide the “RAIL-GEAR” into the “BASE-PLATE”.
2. Insert the “KEY” in the “RAIL-GEAR”, it should fit snuggly into it.
3. Remove the screws from the existing light switch cover. (You can either keep the cover in place or remove it.)
4. Screw the “BASE-PLATE” over the light switch. You'll need to slide the “RAIL-GEAR” up or down to gain access to the screws. Validate that the “RAIL-GEAR” still slides easily, if not try loosening up the screws a little bit. 
5.  Install the “COVER-PLATE” over the “BASE-PLATE”.
6. Glue the 3 parts for the lever together (Gear/Handle/Wood)
7. To install the lever, place “RAIL-GEAR” and Lever as shown below then use the Pin and Clip to secure it in place.

It works for this type of switch:

Here’s the list of filaments I used to make this:

• Bambu PLA Sparkle Slate Grey
• Bambu PLA Sparkle Onyx Black
• Polylite PLA Steel Grey
• Bambu PLA Matte Dark Brown