For your dandruff, I recommend using a medicated shampoo containing generic active ingredients such as ketoconazole, zinc pyrithione, or selenium sulfide. Use it two to three times a week, leaving it on your scalp for about five minutes before rinsing thoroughly. Regarding grey hair, unfortunately, medicated shampoos cannot reverse or treat greying, as it is largely determined by genetics and ageing. However, premature greying can sometimes be linked to nutritional deficiencies, such as Vitamin B12. I suggest consulting a doctor for a simple blood test to check your vitamin levels, and focus on a balanced diet to support your hair health.