You would enter your 529 contribution in the state taxes section of your return.
When you start your New York return, you will be taken through several set up screens asking about residency. Eventually, you will come to a screen that says Changes to Federal Income.
On the Education adjustments section of this screen, the first option is 529 Savings Activity. Click Start here and then enter your 529 contribution.
Remember, your 529 contributions aren't deductible for federal tax purposes, only state.
