Yes, you can still amend your prior-year returns to include these items.
Please see the TurboTax Help article How to amend (change or correct) a return you already filed for guidance.
Generally, for a credit or refund, you have to file Form 1040-X within three years, including extensions, after the date you filed your original return, or within two years after the date you paid the tax, whichever is later.
