It can be tricky. To amend a return you did somewhere else or you don't have the original .tax file, 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.
What year? For the current year you can use the online version by first recreating the original return exactly as filed. Then pay the fees and say to mail it and print it out so it think you filed it. Then when it matches every line you can amend. How to Amend the current year
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-federal-tax-return-current-year/L7eS6o1qh_US_en_US?uid=lfunevhk
Or you can buy the CD/Download Desktop programs here,
https://turbotax.intuit.com/personal-taxes/cd-download
CAN I USE TURBOTAX TO AMEND IF THE RETURN WAS PREPARED SOMEWHERE ELSE?
If you did not use TurboTax to prepare your tax return, it is possible to amend the return using TurboTax but it will really be a pain. It would be better to use the software or service used to file originally. If a paid preparer made a mistake on your tax return, that tax preparer should do the amended return for you at no charge.
In order to use TurboTax to amend your return, you need to purchase the desktop software for the tax year and re-create the return EXACTLY as it appeared when it was filed with the IRS/states. Every line has to be the same. Then you have to "trick" the software into thinking you filed by saying you will mail the return. (but do not mail it) AFTER that, you use the software to prepare a Form 1040X, which has to be printed, signed and mailed to the IRS. It takes the IRS about 4-6 months to process an amended return