Easily done. Try some vinegar mixed with water or rubbing alcohol. Bleach might do it.
Perhaps some crushed vitamin C tablets in clarifying shampoo - don't laugh, this mixture is good for taking hair dye out of hair - it might work on walls too.
If it’s blonde dye, it could have bleached it. What colour is the wall?
Those magic eraser things are really good, but can take the paint off if you go over board