Since it is too late to efile the AGI is no longer needed ... to file a 2018 return you must print, ink sign and mail it in. 

How to file a prior year
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25...

Did you start an online return last Year? How to finish a prior year online return
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...

I just received a W-2 from a company I quit working for in 2019.  Did not realize I had income from them.  What do I do?

If you need to make changes to a return that was already filed and accepted, you will need to amend your return. Please click here for instructions.