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.
get Form 1040-X from IRS website and mail it in with your 8606, which you can also get in fillable PDF.
On Form 1040-X check the box for the year of the Form 8606 that you are submitting.
Note: when you are not changing any dollar amounts on your amending 1040-X, you can leave all the lines 1-23 EMPTY.
Part III explanation: "correct prior years Line 2 of Form 8606 ".
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