What? First of all, a 2018 return cannot be rejected now, because you cannot e-file a 2018 return. E-filing for 2018 has been permanently closed since October of 2019. If you need to file a 2018 return it has to be prepared on 2018 software and it has to be mailed.
As for 2019--if you did not yet file 2018, then you will not have a 2018 AGI to use to e-file 2019, so you have to try to use "zero" instead. if zero will not work, then you have to print sign and mail 2019.