This seems to be the only relevant part of the pictures you posted:
It seems to show that the LED connections are independent of the switch connections.
To decrease LED brightness, you decrease the current thru the LED. Since you didn't actually post or link to any real specs for this switch, we don't know whether there is a bare LED inside, what its forward voltage is, or whether there is a resistor in series.
In any case, adding a resistor in series externally should reduce the brightness. Without specs we'd be guessing at the value. Try in the range of a few 10s of Ohms to a few 100 Ohms and stick with what you liked best.