I still disagree that 1040X is necessary because you are NOT filing a 2018 tax return - you filed that in 2018 and you are not changing anything on that which is what an amended is - a change of what was filed and you are not changing anything. You are just supplying a missing form for that already filed tax return, but you are not amending anything.
Taxpayers have been sending stand alone 8606 form for years without problems, but if that is what the IRS wants then just follow their directions. (I would not amend using TurboTax - you can just print a blank 1040X from the IRS and manually fill it out since they told you to leave all the tax information blank.)
2018 1040X
https://www.irs.gov/pub/irs-prior/f1040x--2018.pdf
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
