You have to switch to the Desktop program to fix it.  Why did it reject?  Some things are only needed For Efiling and don't need to be fixed since you can only print and mail now.

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 had similar problem with my 2018 1040.  I also filed an extension for 1040.

On my return Turbotax forced me to amend and create a 1040X.

It won't change the numbers for 2018 1040 the tax was not finalized and filed.

Hope this helps.

You are never FORCED to do anything ... you may have downloaded the amendment program which expects you to amend the return ... so if that is the case and you do not need to send in the 1040X you can ignore that form in the tax file and simple send the 1040 form that is also in the account along with all other forms/schedules and attachments required for a mailed in return. 

@noors786 If you prepared a 1040X to "fix" a rejected return that was a mistake.  That is NOT what you do to fix a rejected return.  You only prepare a 1040X if your return was accepted and fully processed by the IRS, and then you need to add or correct something.

All you needed to do was make a correction to the tax return using the desktop software if you were past the deadline for using the online software.  Then the return had to be printed, signed and mailed.

What did you do to "file" that return?  After October 15, 2019 e-filing closed permanently for 2018 returns.  And a 1040X can never be e-filed.  You may need to post back and tell us what you did so we can help you sort out the mistake you made.  Even if you mailed in the 1040X, since the IRS has not received an "original" return from you, it is going to cause confusion and be a problem for you.

poster has other question ...   https://ttlc.intuit.com/community/user/viewprofilepage/user-id/668306