Amchoor or Amchur Powder is tangy in flavour so you substitute it with any spice which is tangy like tamarind powder or lemon juice. Tamarind powder can be one of the best substitute of Amchoor / Amchoor powder.
For the homemade recipe of tamarind powder follow the following link:
Tamarind Powder Recipe
For the homemade recipe of lemon juice follow the following link:
Lemon Juice Recipe
or alternately you can make homemade amchoor powder as given in the following link: