It has been suggested that apple cider vinegar placed in a spray bottle, then sprayed on your head/scalp for 20 minutes would be helpul in combatting the fungus/dandruff on your scalp. Then proceed to wash hair as per usual.
I would add that many of the hair products on the market simply aggravate/increase dandruff instead of combatting it. Try some herbal shampoos. I use a product made by nature clean, which uses no chemicals