SI1143 gain change

Hi,
I am trying to do Ambient Light Sensor (ALS) measurements for one of my projects. I am using SI1143 chip as a sensor and reading the datasheet I understand that I can change the gain or vis and IR photodiode as per the user requirement. But I am unable to do so due to my limited knowledge of programming. Can anyone throw some insights on this? I'd really appreciate your help.
I have attached the Si114 library file which I am using.
Thank you.

SI114.h (11.2 KB)

reading the datasheet

Link please

Hi, The link for the datasheet is