If your employer reimbursed less than the full amount of your tuition, you can still amend your return. You can amend your return and input the information from your 1098-T, you will enter it exactly as it appears on the form, as you continue through the interview portion for the 1098-T, it will ask about your employer-provided assistance so that you can account for the amount that was reimbursed by your employer.
Since you have already filed your return, you'll need to wait for your tax return to either be rejected or accepted, if it is rejected you can add your Form 1098-T, correct any other errors on the return and resubmit it. If it is accepted, you will need to amend your return to include the Form 1098-T. You can not e-file an amended return as this cannot be filed electronically. The form is only filed on paper, so it will need to be printed and filed by mail.
Please see the following TurboTax FAQ for instructions on how to amend your 2016 tax return, if necessary, in TurboTax.