If you need to make a change to a tax return that has already been filed, whether for this year or for a prior year you must file an Amended Return (1040-X)
You have to use the software appropriate for that year.
The online software for prior years is no longer available. You may purchase the desktop software here: https://turbotax.intuit.com/personal-taxes/past-years-products
Generally, to claim a refund, you must file Form 1040-X within 3 years after the date you filed your original return or within 2 years after the date you paid the tax, whichever is later.
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