If you used TurboTax to complete and file the tax returns then you can use TurboTax to amend the returns. TurboTax supports amending tax returns for tax year 2018 thru 2016. A federal amended tax return, Form 1040X, can only be printed, signed, dates and mailed to the IRS.
See this TurboTax support FAQ for amending the tax return - https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...
Go to this IRS website for free federal tax forms, schedules and instructions - https://apps.irs.gov/app/picklist/list/priorFormPublication.html
