In this video

Using a long-handled, stiff-bristled scrub brush (or a squeegee with a scrubbing side, as seen in the video), begin to thoroughly scrub the concrete steps. Apply firm pressure and use back-and-forth motions to agitate the detergent and work it into the pores of the concrete. Pay close attention to areas with heavy grime, moss, or visible stains. The goal is to create a good lather and physically lift the dirt from the surface.