To clean a drill. you first need to open it up. Before you touch anything, please make sure not to have your drill plugged in. Remove the screws holding it together, and place them in a safe container. You may see a lot of dust inside due to the amount of drilling done in the past, so we recommend you clean up the surface of the drill before you get stuck in.
Be careful that you don’t damage the gearbox whilst fiddling inside, as the parts inside are very fragile. Make sure if you move any wires, that you also place them where they originally were also. Once you’re done, place all the screws back into their rightful positions and secure tightly.