If you are taking the itemized deduction on your tax return (federal side), reduce the property taxes you are claiming as a deduction by the amount of the Tax Relief Payment you've received. That's all you need to do. If you are taking a standard deduction, you do not need to enter it on your return at all.
The New York return section may ask you if you received a payment or the amount, but that does not transfer to the itemized deduction. You must report the amount by adjusting your property tax in the main itemized deduction interview.