Thanks for writing in.
Greying of hair is quite common problem.
There is no medicine to make white hair to turn black again.
However medication is available to prevent further greying.
Few specific tablets and lotions containing biotin
and multivitamins ca stop greying of hair.
Few hair serums and lotions can be helpful.
To start with you can take B10 cure tablets.
I encourage you to visit a qualified dermatologist
for proper advise and treatment.
Hope this helps.