You add the string, its represented by the purple line in the pic. It is not part of the file. The string is secured to one side of the plate with a knot trapped in the hole and moves freely on the other side. Pulling the strings turns the light on and off. This screws on top of the existing switch plate, the grooved plate screws to the wall so kids cant get caught in the cord. File untested.
I have built one by hand and it works but my 3D printer isn't here yet and I haven't tested this file yet. Hopefully I got all the holes in the right places. Thank you Autodesk for keeping Tinkercad alive!!