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-filed/01/25588
And see this IRS web reference regarding incorrect 1099-R's: https://www.irs.gov/taxtopics/tc154