If the soap scum hasn't hardened, wiping it away with a cloth or sponge should do the trick. If it has hardened, remove it by scrubbing with a mild abrasive, lemon oil, ammonia or a mix of vinegar and dishwashing detergent.
Soap scum is a mix of minerals from tap water, body oils and soap residue. It's usually a dirty gray color and builds up over time. It's commonly found on shower and tub walls and floors, on shower curtains and underneath hair care containers.
To tackle hardened soap scum, sprinkle a damp sponge or cloth with borax or baking soda or make a paste of powdered laundry detergent and water in a 1:1 ratio, and then apply the paste to the scum, Scrub using a circular motion, making sure to rinse well when done. If you use baking soda, follow up with a cup of white vinegar poured down the drain to help clean it.
An alternate approach is applying lemon oil, vinegar mixed with a couple of drops of liquid dishwashing detergent or ammonia to help dissolve the stain. Spray or wipe the cleaning agent onto the soap scum, let it sit for 10 to 15 minutes, and then scrub and rinse as if using an abrasive. If using ammonia, wear gloves to protect the skin and be careful not to mix it with any cleaning product containing bleach, or else dangerous fumes occur.