How do I correct an error relating to the american opportunity credit

You will need to get back to the Education Credit portion of your return and go through the interview screens again so that you can change your answer to that question. 

To get to your Form 1098-T you can follow the instructions listed below:

•  Sign into your TurboTax Online account
• Choose to Continue your return/Take me to my return
• Click on Federal Taxes
• Click on  Deductions & Credits
• Click on  "Check for more tax breaks" 
• Click on "Skip to all tax breaks"
• Locate the section titled, "Education"   and click to "Show more" 
• Click to Edit the area titled Expenses and Scholarships (Form 1098-T)  and  go through this portion of your return to change your answer to how many years of college you have completed at this time