How to calibrate the MLX90616 IR temperature sensor?
Quite simply, you need to build the prototype (or complete) system around the MLX90616 that includes the appropriate (likely microcontroller) interface and processing, then you need to take measurements against objects of known temperature and emissivity. With that data, you can develop coefficients/constants to use in the function that translates the MLX90616 digital output value into a temperature value.