Finish entering your information into your tax return, select File in the left menu, and follow the instructions until you can select the Transmit my returns now button. You will need your 2017 AGI to e-file your return.
you can find your 2017 AGI:
- In TurboTax Online or the mobile app under Your tax returns & documents
- On your originally-filed 2017 tax return, form 1040 (Line 37), 1040A (Line 21), 1040EZ (Line 4), 1040NR (Line 36), Form 1040X (Line 1, column A)
- By ordering a free transcript of your return on the IRS Get Transcript site or buying a full copy of your return by following the instructions here.