I learned this year that I was issued a 1099-R for a previous year that I was unaware of. Do I need to file an amendment?
Yes. You need to amend the tax return for the year in which you received the income reported on that 1099R. Eventually the IRS will send you a letter if you do not report the income--it was reported to the IRS.
A 1040X cannot be e-filed. It must be printed and mailed. It will take about 4 months for the IRS to process an amended return. It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.
Wait about 3 weeks from mailing and you can check the status of your amended return:
Yes, the Form 1099-R is to be reported on your tax return.
See this TurboTax support FAQ for amending 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-...