The best non-technical method used to adjust the back up lamp switch is to place the shifter in reverse, attach the switch rod to both the switch and the reverse rod and then move the switch until the back up lamps come on.
Installation of the rod is easy if it is installed in the correct hole. There is only one hole in the shifter lever, but there are multiple holes in the switch and the rod installs in the long lever with the single hole. You’ll notice there is a divot above the hole in the picture below.
Corvette Back Up Switch Assembly Procedure for all cars with 4 speed transmission. Supporting Documentation