The 1098-T is used to claim an Education Credit.  You do not have to claim the credit. 

Since you've already filed, you cannot add it until your return has been processed by the IRS and you have received your refund. 

However, you could go through the TurboTax Amend feature and add the 1098-T just to see how it would effect your taxes.  If you decide to Amend your 2017 taxes, then you will follow the instructions to mail after you receive your original refund. If you choose not to Amend, nothing has really been done.

Here is the information on how to Amend your return:

https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed