Roast it with turning it occasionally till it gets black from all sides.
(Instead of roasting, you can boil it in pressure cooker. Peel the mango and pressure cook it with some water for 2-3 whistles. Pressure cooking time may vary as per size of mango.)
Let the mango cool completely.
Then peel the skin off. Skin will come out very easily.
Roughly chop it. Most of the part will be very soft and pulpy.
Making raw mango chutney:
add this cooked mango to the blender along with rest of the ingredients .
Grind it into a smooth puree. (Do not add any water)