How to find it

In what context and based on what information? That's very ambigous and no one knows what you're doing or what you have available to figure it out with.

I also don't know what's meant by net interest income. A net is generally implying that you had some amount but subtracted something out for some reason, to get a net amount that is less than the original. (Like your net paycheck is gross less taxes.) If you are subtracting something from interest income, we can't know what unless you tell us what you're doing. Interest can be applied to a lot of different things in a lot of different ways.