Just take a mini N.O. (normally open) switch with two terminals and a 3mm LED and wire everything according to the schematic of step #3

My suggestion is to put the LED near the end of the plastic cover and the button just over the keyboard, then make two little holes in the corresponding places of the front cover for each.

Use a screw to hold the LED and a little bit of hot glue to secure the switch and the wires.

Re-assemble the front cover as per figure 2.