There is no magic spray or device that you can use to make them go away. Some people try to sell fake plastic owls or plastic hawks to get rid of pigeons, but that doesn't work. They also try to sell ultrasonic
First, empty the feeder and get rid of any old food and other debris. Submerge the feeder in a container filled with water and some dish soap and clean it with a brush or dish rags. Make sure to clean every part and to give it a good rinsing. By now, your feeder is pretty clean ...