Why did it reject? If it was for the wrong AGI you don't need to fix that. AGI is only needed to efile and it is too late to efile. If you need to fix something else you need to finish in the Desktop program. You need to download the .tax2019 and open it in the Desktop program. You need a full Windows or Mac computer to install the Desktop program.
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-...
If you paid for the Online version you can ask support to give you the Desktop download. Contact Customer Service 5am-5pm Pacific M-F
https://support.turbotax.intuit.com/contact/
