You would enter your estimated tax payments in the Deduction & Credits section of TurboTax. It would be under the "Estimates and Other Taxes Paid". After you enter your income into TurboTax and continue to the Deductions and Credits Section, you will see a link, "Show me more deductions" at the bottom of the Blue section. Scroll down till you find the "Estimate and Other Taxes Paid" section then "Show More". The first option is Estimate Tax Payments. Continue through and enter your estimated tax payment in the quarter then were paid then "Continue".
You may be able to get any underpayment penalty waived if you have not requested a waiver in the last 3 years.
Click HERE for information from IRS.gov