Brief Answer:
Use ketoconazole shampoo.

Detailed Answer:
Hello dear, welcome Ask a doctor's service.
I read your query and here is my advice.

There are different types of shampoo in the market which can be used to treat dandruff.
There may be shampoos containing tea tree oil, zinc, selenium or coal tar and you can use one of them. Keep the shampoo for 5 minutes before rinsing to do its effects.
Also using cinder vinegar, or baking soda is advisable. You can also coconut oil to massage the hair.
If these methods don't work you can use ketoconazole shampoo, antifungal shampoo to wash your hair.
Keep it 5 minutes before rinsing.
Use it every day or as often as you get your hair washed.
You may use it for at least two weeks.

Hope I have answered the question.
Let me know if I can assist you further.

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