If you have already submitted your return and it is Pending, you will need to wait until it is either Accepted or Rejected. If your tax return gets rejected for any reason, you will be able to add your 1098-T and then resubmit your tax return. If your tax return is already accepted, you will need to file an amended return (after the IRS processes the original return) in order to add your documents.
How do I amend my 2019 TurboTax Online return? This link gives instructions on how to amend. If you do need to amend, wait until your original return has been processed in order to avoid any unnecessary delays.
*** If you are claimed as a dependent on your parents' tax return, they can enter the 1098-T on their return as they would be eligible for the tuition credits, not you.