This question will be asked within the 1098-T section:
2.) Deductions & Credits
3.) Scroll down to Education
4.) Click Start or Revisit next to Expenses and Scholarships (Form 1098-T)
If you have already entered this information, you will see Here's Your Education Summary. Click Edit next to Education Information. There will be several questions within this section pertaining to how many years and whether or not they have already received the American Opportunity Credit.
If you have not yet entered your 1098-T into TurboTax, these questions will be asked as you proceed to enter this form into TurboTax by following steps 1-4 above.