Form 8606 can be filed by itself when you are not required to file 1040.
Otherwise attach 8606 to your tax return.
Having amended you have a new form that was not on your original return.
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1040x- How to file
Do not include your old 1040 nor your revised 1040 because the Form 1040X reflects any changes there and becomes your new tax return.
Include any new/corrected document only if it shows federal tax withheld, and include in order only those Sequence Numbered tax forms and Schedules that changed or were added due to your amendment.
Attachment Sequence Number is on all the forms and Schedules that come after 1040.
Mail to the address shown for your location in the Instructions for Form 1040X
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In your case your amendment has two forms: 1040X and 8606.
The Explanation on Part III will let the IRS know why you are filing.
