The short answer is you can't. Flashlight reflectors are too cheaply made and are too fragile.
High-quality first-surface mirrors, like you find in astronomical telescopes and some telephoto camera lenses, are made by placing a ground and polished glass substrate into a vacuum chamber. Very pure aluminum is vaporized by heating, and it condenses like dew onto the glass in a layer a few microns thick. Aluminum this pure is very soft and is also chemically reactive, so as soon as the coating is deposited, it is immediately protected with a very thin transparent overcoat of quartz. Some of the newer high-efficiency reflectors use more complicated multi-layer overcoats. These mirrors can be cleaned, since the overcoat material is non-reactive and fairly hard. Even so, it takes special materials and great care.
All of the flashlight reflectors I've seen also use evaporated aluminum, but onto molded plastic instead of glass, and there is no protective overcoat. As soon as the aluminum hits the air, it forms a thin protective layer of clear aluminum oxide, but it is extremely fragile. Wiping the surface easily peels the oxide off, mottling the surface. Rubbing the exposed aluminum, even with soft cotton, causes microscopic scratches which appear cloudy to the naked eye. Exposing the surface to even pure distilled water reacts with the aluminum, causing a thicker cloudy-appearing oxide layer to form. Most solvents will attack the plastic substrate and leave residues. Tap water and skin oils contain salts which will etch and stain the aluminum.
All things considered, the only choices are to leave the reflector strictly alone or to replace it. After all, it is a cheap item.
IDK what this means but it was funny!
