Where can I enter the CNIL value stated on my last assessment?

I know there is a place to fill out a form or schedule or table with data from many previous years, that will calculate the CNIL. That's impossible to do, accurate data for that doesn't exist. However CRA tells us each year, on our assessment, what our CNIL is. So it should be possible to just enter that value somewhere. Where can that be done?

Thanks!

Andy