Yes, you can amend your tax return. But first, wait until the IRS accepts or rejects it.
If rejected, simply log back in and make the necessary corrections. If accepted, then you can amend your return.
However, it will be best if you first wait to receive your
current refund before you amend. You can only mail in an amended tax return. Please
note: A Form 1040X, Amended U.S. Individual Income Tax Return can take up to 16
weeks to process once the IRS receives it.
After you have received your refund, please read this
TurboTax FAQ about amending your 2018 tax return: How to amend (change or correct)
a return you already filed.
