How To Get Rid Of White Hair On Chin?

hi i am 32 yrs old and a year back i found two three white hairs on my chin,so i cut it but now it increased in one year and it becomes 12-14 in numbers and mostly in chin.my eating habits are normal my weight is 72 kgs and my height is 5"9'.how can i stop further greying of hairs in my beard,do i have to go for any treatment,and can my already greyed hairs on chin be black as it was before.