File a PA tax return. Any withholding in excess of the tax you owe will be refunded to you. Are you a resident of PA or another state and have you prepared a federal return yet?
Enter you w-2, including the withholding on your federal tax return, and TurboTax will automatically transfer that to your PA state return. After you finish the federal return, go through the PA state interview. If you owe no tax to PA, the full amount will be refunded.