Below is information on finding your 2017 return in TurboTax and where to find the AGI amount on it:
https://ttlc.intuit.com/replies/3301618
Note that if you do not have access to your prior year return, you can request a free online
transcript of your 2017 tax return from the IRS. The transcript will
include your 2017 AGI amount on it. Use this link: IRS Get Transcript