To amend a return you did somewhere else, you would first have to fill out Turbo Tax like you are doing the original return and pay for it. You have to recreate the actual wrong original return. Then when it matches each line that you really filed you have to tell Turbo Tax you will mail it so it thinks it was filed. Then you can amend it.
You have to buy the 2018 Desktop program. You need a full Windows or Mac computer to install it on. Buy the download here
https://turbotax.intuit.com/personal-taxes/past-years-products/
You can recreate the original return using the Forms Mode. Then say to mail it. How to amend a Desktop return,
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return-in-the-turbotax-cd-download...
