Hi @anbriosso ,

Use a 1:10 solution of chlorine bleach diluted in water (1 part bleach - 10 parts water) and a stiff bristled scrubbing brush to remove the mould. Chlorine bleach is available from hardware stores etc.

Be safety aware when doing this and wear protective eyewear and gloves etc. Follow the instructions on the label of the bleach container.

After it is clean you may want to consider repainting the wall. Try applying a mould action pre-paint treatment before painting. Then use a mould resistant paint.

Also check if any water that gets onto the balcony area can drain away and doesn't just stand there keeping the area damp.

Just what I'd try.