You can only file a federal amended tax return after the original federal return has been accepted by the IRS.
Amended federal tax returns can only be printed, signed, dated and mailed to the IRS, they cannot be e-filed.
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-...
