Filing an amended return is only for your taxes I believe. You question is tricky but can be simple if you speak with a turbo tax live professional online.
It is possible to claim a newborn as a dependent only if they were born at any time during the tax year.
"Can you add a child to your taxes after filing?
Yes. You can file an amended return this year and you may add dependents to any of the past three years returns or within two years after the date you paid the tax, whichever is later. To add or change the number of your qualifying dependents, you must do the following: Print and mail all amended returns".
