How can I clean mold off a concrete wall?

Bleach will clean the mold off. Vinegar will kill mold spores. Do not mix the tweo together. The fumes are harmful. Clean with bleach. Rinse well. Then clean with vinegar. Rinse well.

https://www.hunker.com/13415361/how-to-kill-black-mold-on-concrete

Looks like you have more serious issues with the paint on the concrete. I am not sure that is even mold but it does look like you have a moisture problem. Adding paint over concrete is not a long lasting fix if there is excessive moisture. It might be better to remove all the paint and let the concrete just be concrete. It would be much easier to clean.

https://www.hunker.com/12002433/fuzzy-white-mold-growing-in-concrete

https://www.mouldfacts.ca/mold/white-mold-in-basement-concrete.html

Might not be mold- could be this:

https://theconstructor.org/concrete/efflorescence-concrete-cause-prevention-removal/26844/

Connie....Try Krud Kutter (Lowes) and pressure washer

Get Clorex Outdoors at Home Depot or Lowes. It will kill the mold.. Wear gloves when using.

I second Gk and Sawhorse.net. The paint is peeling off the concrete. Mold and algae discolor surfaces but they don't cause paint to peel. You would be better off removing the paint, and staining and sealing the concrete.