As per the instructions quoted above,
the proper way to file Form 5329 is attached to Form 1040-X.
Form 5329 can be mailed by itself only when you are otherwise not required to file a tax return.
After you e-File,
get Form 1040-X from IRS website and mail it in with your 5329 which you can also get in fillable PDF.
check the 1040-X box for the year you are amending.
Note: If you need Form 5329 for Excess you are paying a penalty so you have to enter the appropriate amounts on 1040-X Lines 1-23
Include any other forms or schedules that changed due to your amendment. (currently Schedule 2 Line 8, IRS keeps moving lines around )
Do not include your old 1040 nor your revised 1040 because the Form 1040-X reflects any changes there and becomes your new tax return.
Done this way, you sign 1040-X, not 5329.
@RothExcessPast
