I am an alien resident who mistakenly filed as an alien nonresident using Sprintax. Turbotax seems to only file 1040-X for returns that are done using Turbotax (Form 1040). Do I need to file a new Form 1040 using Turbotax in order to file 1040-X?
Yes, you will file a 1040X. You will not file a 1040. You can create the 1040 to make the amended. Then you can print and mail the amended return.
See About Form 1040-X, Amended U.S. Individual Income Tax Return
Thank you. I tried e-filing the amendment based on the 1040 I just filled out, but the "original amount" column on page 1 is based on 1040, which does not reflect the information from 1040-NR. How can I change those numbers?
You can NOT file the 1040X electronically since you did not file the 1040 through TurboTax and because you filed a 1040NR. You will need to do it print and mail your return. You may have to manually enter some of the numbers if the columns are not lining up as TurboTax does not support the 1040NR so it does not have the ability to match up the columns if the 1040NR lines do not match.