After you file

As @xmasbaby0 said, you will have to wait for your original tax return to be accepted before you can file the amended return; however, you can prepare the amended return now.

There will be two steps:

1. Bring up the amended return.
2. Change the Deduction.

If you want to make changes, or add a document to a tax return that has already been submitted you should follow these guidelines.

• You must first wait until the initial return is completely processed.
• You will have to use the same TurboTax account that you used for the original tax return.
• Once you begin your amendment, you'll see your original return. 
  • The refund calculator will start new at $0 and only reflect the changes in the refund or tax due
  • Only make changes to the areas of your return that need amending.
• You have three years from the date you filed your return or two years after you paid the tax due (whichever is later) to file an amendment

To amend your return:

Sign in to TurboTax

1. On the home screen, scroll down to Your tax returns & documents and 
2. select the year you want to amend
3. Select Amend (change) return, then 
4. Amend using TurboTax Online
   1. If you're told to amend your return via TurboTax Desktop, follow the steps for TurboTax CD/Download below instead.
5. On the screen OK, let's get a kickstart on your amended return, select the reason(s) you're amending and Continue.
6. When you reach Here's the info for your amended federal return, select Start next to the info you need to change.
7. Continue through the screens, make the changes you need to make, and carefully answer the remaining questions to finish amending your return.

To change your deduction method

Many, but not all, states let you take a different deduction than what you took on the federal. 

When starting  State Taxes in TurboTax, 

If your state does have the option to choose differently, we'll ask which deduction you want to take.

1. Open your tax return 
2. select Federal, 
3. then Deductions & Credits.
4. Scroll to the bottom and select Continue.
5. Answer all the questions, until you get to the screen 
6. The screen will show XXX Deduction is right for you
7. At the bottom of that screen, select Change my deduction.
   • You'll see a pop-up showing how much each deduction is worth.
8. If you want to change your deduction, select the one you want. Continue.
9. If you don't want to change your deduction, select Cancel.

  Also see How do I change from the standard deduction to itemized (or vice-versa)?