Painting and staining of your deck is just not required due to the composition of composite decking boards. In fact, if you paint the decking it will just peel away after a short time.
Most maintenance is as simple as a brush, a wash with a cleaning powder or fluid, a rinse and that’s it. Done!
If you have stubborn stains or marks then a light kitchen scourer or fine sand paper or glass paper can be used to restore the finish. Don’t go too hard on it or rub too vigourously. Go steady and be patient. Your deck may need a few weeks to weather back in.
Also avoid dragging heavy furniture across your deck. It will scratch it if the furniture has sharp edges. Even composite decking can be scratched although it is generally hardier than softwood decking.