Black Mold

You need an exhaust fan in your bathroom, and it needs to run from the time you begin your shower until about 30 minutes after your shower. Put it on a timer.

Bleach.

You can buy mold removing products, warm soapy water sometimes helps, and in future you will find leaving a window open when you take a shower, will help ease this from happening, it’s lack of air why this happens! The mold forms from the hot steam if it cannot escape!

spray it with bleach. wear a mask cuz it might make you sick if u use too much.

To get rid of it, use a bleach/water combo to wash it off. Then paint with Kilz to contain and protect. Paint walls, and then, as stated above, put in an exhaust fan.

I had dark matter growning in the damp areas in my shower(that M word is a no-no in real estate circles) and found that bleach mixed with a little dash of dishsoap in a ****** bottle worked well to eliminate it. In a couple of bathrooms where the dark matter has penetrated the caulk around the tub you might need to step up to a stronger solution and substitute pool shock (which is 10% sodium hypochlorite versus the 6% of bleach). They sell pool shock in gallon bottles for just a little more than a gallon of bleach in most home improvement stores (and big W mart stores).

spray soak it with Tilex mold and mildew remover. That stuff works great. make sure the bathroom is ventilated when you do this because the fumes are bad for you. soak the moldy spots, and wipe off with paper towels, then resoak/spray until the mold is completely gone.
Tilex will not ruin the paint. But it is most important to ge the mold out because that is dangerous to your health

No, it won’t harm the paint.