we need more info to be able to help you. can you get to the attic area of the garage, is your garage drywalled or open wall studs and ceiling joist? where is the current switch that controls the existing two lights in the garage? sounds like you want a total of 3 lights with separate switch controls in the garage? Post up with more data and answers to the above. Basically, you would need to get access to the current power source for the two lights you have and route that power to a wall in your garage to feed three switches that you must add and you need to add a third light assembly/box and wire the three separate switches to the three lights.