You will need to amend the 2018 tax return to add the Form 1099-R. An amended federal tax return, Form 1040X, can only be printed and mailed, it cannot be e-filed. The IRS will take up to 4 months or longer to process the amended tax return. If taxes are owed after completing the amended return, you send a check with the amended return when it is mailed. If the amended return has a tax refund, then the IRS will send you a refund check in the mail for the refund, the refund cannot be direct deposited.
The IRS Form 1040X is estimated to be available on 02/22/2019. See this TurboTax website for IRS forms availability - https://care-cdn.prodsupportsite.a.intuit.com/forms-availability/turbotax_fed_online_individual.html
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
Unfortunately, you'll need to amend your return.
Please see the TurboTax FAQ "How to amend (change or correct) a return you already filed," below, for instruction on how to amend your previously-filed tax return.
Please note, however, that Form 1040X, the Amended Return form you need, isn't yet available for filing. The tentative availability date for Form 1040X is 02/22/2019.
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