If you need to amend a Federal income tax return, please refer to the instructions in the TurboTax FAQ: How to amend (change or correct) a return you already filed https://ttlc.intuit.com/replies/3288565
For instructions on amending a previous year's state return, please review the TurboTax FAQ: How do I amend a prior-year state return? https://ttlc.intuit.com/replies/4643391