Question

how will we get milk from curd

Answer 1

Conversion of curd from milk is chemical change. There is formation of a new compound during the curd formation.
The bacteria Lactobacillus when added to milk converts it into curd.The bacteria breakdown the lactose in milk to lactic acid.This increases the acidity of milk due to which the milk protein casein coagulates as curd.

The chemical reaction involved is:

C₁₂H₂₂O₁₁ (lactose) + H₂O (water) → 4 CH₃CHOHCOOH (lactic acid)
So we can not get back milk from curd.