Using Deluxe verision
How do I append my 2018 return when 2017 return was amended without creating a new 2018 return?
You can't. You would have to start a new 2018 return to transfer from the amended 2017 return. Or make any changes to 2018 manually. If you have the Desktop program you can switch to Forms to enter the changes. But you will need to find the source worksheet to make the changes on. If you have overrides you can't efile.