I failed to include 8606 in my taxes last year

"last Year"

The proper way to file Form 8606 is attached to Form 1040-X.
Form 8606 can be mailed by itself only when you are otherwise not required to file a tax return.

Did you do a true backdoor contribution that is tax-free, or planned to be?
in that case Form 8606 will show a taxable amount of zero.
Do you have the correct taxable amount on Form 1040 Line 4b and did not take a deduction? (Schedule 1 Line 20)?
If that is all true then only Form 8606 has to be attached.
After you e-File,
get Form 1040-X from IRS website and mail it in with your <year> 8606, which you can also get in fillable PDF under "prior forms".
Note: when you are not changing any dollar amounts on your amending 1040-X, you can leave all the lines 1-23 EMPTY.

Part II explanation: "didn't include Form 8606 with e-File".
Done this way, you sign 1040-X, not 8606.
Do not include your old 1040 nor your revised 1040 because they are identical.

To create Form 8606 with TurboTax enter your IRA contribution and make the non-deductible election.

@davenj 

Just to add what fanfare has mentioned previously, to add 8606 to your return:

1. Open or continue your return.
2. Navigate to the IRA contribution section:
   • TurboTax Online/Mobile: Go to IRA contribution information.
   • TurboTax Desktop: Select Search Topics. Search for and select IRA Contribution Information.
3. Proceed through the IRA section, answering questions as you go.
4. Answer Yes when you reach the screen Choose Not to Deduct IRA Contributions
5. Select Continue.
6. We'll generate and fill out the 8606 behind the scenes.

Thanks, but I don't see a way to create an amended return with an 8606.  

If you want to make changes or add a document to a tax return that has already been filed and accepted by the taxing agency, you should follow these guidelines. 

• You must first wait until the initial return is completely processed.
• You will have to use the same TurboTax account that you used for the original tax return.
• Once you begin your amendment, you'll see your original return.
• The refund calculator will start new at $0 and only reflect the changes in the refund or tax due
• Only make changes to the areas of your return that need to be corrected.
• You have three years from the date you filed your return or two years after you paid the tax due (whichever is later) to file an amendment

Select your product below and follow the instructions. 

Amend TurboTax Online 

Amend TurboTax CD/Download 

Thanks.

How do I report the conversion of an IRA distribution to a Roth within the 60-day window in Turbotax? 

Contact TurboTax Support to find out how to begin a 2023 amendment if it is not apparent.

you probably would not be able to e-File 2023 Form 1040-X with TurboTax, although one forum participant  claimed success.

You don't need that.

Start a New Return and make an  IRA contribution. Print the form.

Then proceed as I said above

By the way if you amend your return with TurboTax, you will lose your "original return",

unless you save or print your copy first.

@davenj 

Thanks. I have generated an amended return, but one of the changes I would like to make is to report the conversion of an IRA distribution to a Roth within the 60-day window. I have reported the IRA distribution, and Turbotax generated an 8606 for the amended return. But I don't see any place to document the conversion.  Is it necessary to report?  

"How do I report the conversion of an IRA distribution to a Roth within the 60-day window in Turbotax?"

you would not report that. Keep records showing you operated within the 60-day window.

@davenj 

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@davenj 

Never Mind  !

@davenj 

Excellent.  Thank you.