Hi! Great question!
In order to claim a deduction you missed in a previous tax return you already filed, you would need to amend the return from the previous year(s). Assuming you used TurboTax to prepare your previous return(s), please follow the instruction in this article: How do I amend my federal tax return for a prior year? You can also amend any state return using the same procedure.
You have 3 years after the date you filed the original tax return or within 2 years after you paid the tax due on the original return, whichever is later, to amend. See this TurboTax article: What is the deadline for filing an amended return?
I hope this helps.
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