I have to amend my return because I filed a 1040A and should have filed a 1040NR. When amending through turbotax and asked why to amend I do not see an option for this.

You amend by filing a 1040NR together with a 1040X. You cannot do this with TurboTax. TurboTax cannot prepare a Form 1040NR. TurboTax has a partnership with Sprintax to prepare a 1040NR federal tax return and corresponding state tax return for certain categories of nonresident aliens. Go to the following link for the details of who can use Sprintax, and to get started. If you do not meet the requirements for Sprintax, you will have to find another way to prepare your 1040NR.

https://www.sprintax.com/non-resident-alien-tax-1040nr-turbotax.html

Here is what the IRS instructions for Form 1040X say to do if you filed Form 1040, 1040A, or 1040EZ and you should have filed Form 1040NR or 1040NR-EZ instead.

• Enter your name, current address, and social security number
  (SSN) or individual taxpayer identification number (ITIN) on the
  front of Form 1040X.
• Don't enter any other information on page 1. Also, don’t
  complete Parts I or II on page 2 of Form 1040X.
• Enter in Part III the reason why you are filing Form 1040X.
• Complete a new Form 1040NR or 1040NR-EZ return.
• Across the top of the new return, write "Amended."
• Attach the new return to the back of Form 1040X.