Last year I filed jointly with my spouse but we are separated and filing separately this year. I need only my AGI from last year for a state tax break. How do I find it?

We get a "kicker" from the state this year based on how much our AGI was the previous year. I filed with TTax and my return only shows me the aggregated AGI. I'm supposed to say how much of the prior year only belongs to me. I don't know how to find that given that we shared deductions on our house and such. Help!