If you’ve already filed your taxes without Form 8962 but think you need to include it, don’t amend your return. Wait until the IRS sends you a notice requesting the form before you act.
If you’ve already received a notice from the IRS requesting Form 8962, you’ll have to add a Form 1095-A to your return in TurboTax, print Form 8962, and mail it to the IRS. Instructions are in the link below - and it is a current link. This is an old thread. so old links still show. If you ever need to start a new thread, here is a shortcut link.
Here is an updated link @SarahBowman
The IRS is requesting Form 8962 for 2021