If you are talking about the Premium Tax Credit, which is the subsidy that pays down your premiums under the Affordable Care Act ("Obamacare"), then when you enter the 1095-A that you received from the federal or state marketplace, TurboTax will compute the amount that you were overpaid and add it to the taxes due on your return.
If you got marketplace insurance and didn't get a 1095-A then you need to get your 1095-A before you file your return.