I did my 2018 return by hand and made a mistake. How do I file a 1040X using Turbotax?

[rjs]

An amended return uses the original return as a starting point. To prepare an amended return with TurboTax, you would first have to recreate your original return in TurboTax, making sure that it exactly matches the return that you filed, then amend the recreated return.

An amended return (Form 1040X) cannot be e-filed. You have to print it, sign it, and file it by mail. It takes the IRS up to 16 weeks to process an amended return.

Don't file an amended return until your first return has been processed and you have received the original refund.

[VolvoGirl]

And you might need to use the Desktop program so you can recreate the original hand return you filed.  You might have to make overrides using the Forms Mode.  You can buy the Desktop CD or Download here,

https://turbotax.intuit.com/personal-taxes/cd-download/

Then when it exactly matches what you filed and amounts are the same for every line on the 1040 tell Turbo Tax you want to file by mail and print out the original return so TT thinks it was filed, then you can do the amended return.

[Critter]

What was the mistake ?   Many the IRS will correct for you automatically so don't amend anything until the original return has fully processed.  

And it may be cheaper and easier to complete the amendment manually ... https://www.irs.gov/forms-pubs/about-form-1040x