Lemon is really beneficial for the hair and it is told that it helps with dandruff.
All you need to do is apply 2 or 3 spoons of lemon juice by massaging and then rinsing your hair with warm water with a few drops of lemon juice.
You can do this until the dandruff problem is resolved.
But, do not forget that lemon is a natural bleacher. It may lighten your hair color.