Yes, you can still file, but you would have to print and mail. You can't e-file without your 2017 AGI.
Here is where to find it:
If you prepared in TurboTax Online, here is how to access your prior return:
1. Make sure you’re signed in to your TurboTax account.
2. Select Tax Home from the left menu.
3. Scroll down to Your tax returns & documents and select 2017.
4. Select View adjusted gross Income (AGI)
If you prepared your tax return in TurboTax CD/Download, it should be saved on your computer.
If you prepared your tax return through other software, you can request a transcript from the IRS.
Follow this link: Get a Transcript
If you filed your tax return after October, 2018, use $0.
For more information, including a picture reference, follow this link: How to Find Last Year's AGI