|The way a switch works is it breaks the ‘black’ wire and cuts the power to the light. Turn off the electrical power first!! You would have to run a wire from the switch (up inside the wall), across the ceiling to the light fixture. If you have attic access this is easier because going from the inside the wall to inside the ceiling is the hard spot because of the house framing in the corner. Once the wire is run, then put a box and switch at the wall location connecting the black and white wires to the side screws and the copper to the ground. If it is a metal box then you must run the ground wire to the box ground screw too. The other end inside the light fixture box, goes to the black wire that is connected to the fixture. Disconnect the black wire, then connect it to the black wire of the switch wire. Then the white goes to the black wire of the fixture. Ground to ground. You’re done, put it all back together and power it up!
Remember, if you are not sure of what you are doing, then consult a licensed electrician in your area.