Follow the instructions in the amendment program ... you will revisit the 1099-R entry that you did before and change your answers to the follow up questions in that section. This time you will say YES to making a repayment.
See this TurboTax support FAQ for how to amend a tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...
