Dip a paintbrush into the latex paint you used to paint your walls. Use the leftover color to ensure it will be the same shade or purchase the same shade from a hardware store.
Brush the paintbrush against the sides of the paint can to remove most of the paint. This will prevent you from having to remove the paint once you've placed it on the wall.
Brush the paint directly over the shiny spot. Don't over-smooth the paint or brush over one area too many times as this will actually cause brush marks. The latex paint will harden as it dries and if you brush over it, the bristles will push into the otherwise smooth surface.
Repeat the process with the rest of the shiny spots.
Let the paint dry completely.