how to set a ADC current offset for the other PIN

In my application,I need detect the bus current,so I add hall sensor on bus line.the1.65V±1.65V output signal PIN of hall sensor connects ADC-B5 PIN of 28069M.

In <motorware_hal_tutorial>,it can guide how to add a Potentiometer Read,but it can not teach how to manage "offset".  it should have a ADC current offset for bus current such as 

#define I_A_offset (XXXXXX) 

#define I_B_offset (XXXXXX) 

#define I_C_offset (XXXXXXX) 

 #define I_bus_offset (XXXXXXX)

But how to make  I_bus_offset be effective in motorware ?