You can amend your Federal return only.  You only have to amend a State return if when you amend your Federal it affects your State return.  Go back into your return & choose Amend an already filed return, the Federal amendment form is 1040-X.

Wait until you receive your refund to amend. If you owe, you can amend e-filed returns if they've been accepted and paper-filed returns after they've been mailed.

Once you begin the amendment process, you'll see your original return. Only make changes to the areas of your return that need amending. The refund calculator will start new at $0 and only reflect the changes in the refund (or tax due).

You have three years from the date you filed your return or two years after you paid the tax due (whichever is later) to file an amendment.