Begin by smoothing the aluminum foil over the bead or the end of a pen to make it a rounded shape for the back of the light. Press the metal against a soft embossing surface and work the top of the reflector into the shape of half a capsule. When you have the metal shape embossed, trim it to shape with scissors.
Extend the wire on your led if necessary, and test fit it into the reflector to make sure the reflector fits the LED.
