I failed to take a deduction for energy efficient windows and need to amend my return. How do I do this?

First wait until your original tax return has been processed and you have received the refund. Then see the following FAQ for instructions to amend a 2021 tax return that you filed with TurboTax.

How do I amend my 2021 return?

Before you start to amend your return in TurboTax Online, be sure to download a PDF of your original tax return and save it on your own computer. Once you amend it, you will no longer be able to access the original in TurboTax.

The IRS is severely backlogged this year, so expect it to take 5 months or longer for your amended return to be processed.

It's a tax credit (not an income deduction) in the amount of 10% of the purchase price (excluding installation cost) with a maximum credit of $200.  The energy credit is a nonrefundable credit that can only reduce the tax you owe to $0.