You need to enter the non-deductible contribution in the year that the contribution was for in the IRA contribution interview.
You enter the 1099-R in the year converted.
See this TurboTax FAQ:
https://ttlc.intuit.com/questions/4350747-how-do-i-enter-a-backdoor-roth-ira-conversion
2019 and earlier can only be amended with TurboTax using the CD/download version installed on a PC or Mac computer.
It is suggested that it be mailed certified with return receipt (or other tracking service) to verify that the IRS or state receives it.
See this TurboTax FAQ for detailed amend instructions:
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
-- Amended returns can only be mailed - allow 8-12 weeks - can take up to 16 weeks (4 months) for processing.
You can check the status of the amended return here, but allow 3 weeks after mailing.
https://www.irs.gov/filing/wheres-my-amended-return
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
