After you file

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@1967jeff1967jeff wrote:

Thank you so very much for your reply.  But please, if there's nothing to amend, wouldn't it be just plain wrong to file a 1040X?

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I would call the IRS on the number that should be on the letter and discuss it with them.

Unless you deducted the contribution in 2018 and are now changing it to non-deductible (or non-deductible to deductible) both of which would change the AGI and tax then no 1040X is necessary.

The 2018 1040X instructions say:  "Changing your IRA deduction. In Part III of Form 1040X, enter “IRA deduction” and the amount of the increase or decrease. If changing from a deductible to a nondeductible IRA contribution, also complete and attach Form 8606, Nondeductible IRAs.".

And the 2018 8606 instructions say:  "Amending Form 8606
Generally, after you file your return, you can change a nondeductible contribution to a traditional IRA to a deductible contribution or vice versa if you make the change within the time limit for filing Form 1040X (see When To File in the Form 1040X instructions). You may also be able to make a recharacterization (discussed earlier). If necessary, complete a new Form 8606 showing the revised information and file it with Form 1040X"

So again, if you are NOT changing the contribution from deductible to non-deductible (or the other way around), then the 1040X is not necessary.     In addition, you are NOT amending the 8606 since an original 8606 was never filed - you are now simply filing the late original 8606 that should have been attached to the 2018 tax return but was missed and the IRS can charge a $50 penalty for processing a late 8606 which they can waive.