After you file

No you can't get the file anywhere.  You need your original.tax2018 file on your computer.  Or you would have to fill out a new Return like you are doing the original return. You have to recreate the actual wrong original return.  Then when it matches each line that you really filed you have to tell Turbo Tax you will mail it (and probably print it out) so it thinks it was filed.  Then you can amend it.