Fussy eater

How to deal with fussy eater ? My little boy 15 months old weight only 8.1 kg . Recently doesn’t eat anything except mou tou or bread He only drink little milk a day around 150ml only He is not bid eater and since baby he doesn’t like milk Recently dietician suggest give him even chocolate milk or strawberry milk but I still doubt on it Any mummy here experience same situation , any suggestion ?