If you have a copy of your 2018 tax return or if you filed in Turbotax last year, thats your best bet. Your AGI is on the first page. You can call the IRS (look on the irs's website because they removed the number from the post) but be prepared to wait. Its tax season and there will be a que. Also, the IRS may still not give you the info. You would have to verify your identity before they release personal info regarding a taxpayer's account.
You need your 2018 AGI to efile 2019. The AGI is on 2018 1040 line 7. If you filed a Joint return you use the same AGI for each spouse.
How to find the AGI.
If you didn't file 2018 or filed it later in the year then try entering 0 for the AGI. If that doesn't work you will have to print and mail your return.
IRS is 1-800-829-1040 or get a Transcript