NOTE there is still one week to e-File 1040-X if your Form 1040 was ACCEPTED.
OTHERWISE,
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.
Do you have the correct taxable amount on Line 4b and did not take a deduction?
After you e-File,
get Form 1040-X from IRS website and mail it in with your 8606, which you can also get in editable PDF.
Note: since you are not changing any dollar amounts on your amended tax return, you can leave all the lines 1-23 EMPTY.
Part III explanation: "didn't include Form 8606 with e-File".
@joycog23
