Just push the mounting screw for the tip with a thin rod or a small Philips screwdriver, all the way through till it pops off the other side of the shift lever assembly. The nylon washer will be left inside the lever well. Tap the shifter on a flat surface to make it fall out. Don't worry about possibly damaging the washer as it is only held on to the screw with friction. There are no threads on it.
To reinstall the washer on to the screw, just use a hollow tube to put the washer through the screw. Kinda reverse process from when you remove it.....
Frankly, I'm not sure if the nylon washer is really needed, as I suspect Simplex might have put it there so that the whole assembly stays together when it's not mounted on the shifter boss....
You can try it without the nylon washer and tell us if it still works OK......