Can i refile past years taxes? may have missed a elderly parent deduction

[DexterS]

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.