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.
Get Form 1040-X from IRS website and mail it in with your 5329 which you can also get in editable PDF.
Note: When you are not changing any dollar amounts on your amended tax return, you can leave all the lines 1-23 EMPTY.
Part III explanation: will explain to the IRS why you missed the RMD, what action you took that they should waive your penalty. This is required if you request a waiver. Include dates and amounts.
(what you posted here may be sufficient; if IRS finds it "reasonable").
You must use the 20NN Form 5329 for amending year 20NN.
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