I filed my taxes, but I forgot to include a 1098-T form from my community college. Is there a way that I can just add this document to the return that I already filed?

You would have to amend your tax return in order to add the 1098-T to your tax return.  

Since you have already e-filed the return, you will need to wait until the IRS has accepted it. Once they accept it and you have received your refund, then you can amend it by adding the 1098-T.

Once you receive your refund, you can go here https://ttlc.intuit.com/questions/3061514 and get instructions for amending. 

And the instructions are here https://ttlc.intuit.com/questions/2562661 for where to enter the Form 1098-T when you are amending the return.

NOTE: Your 1098-T may qualify you for education-related tax benefits like the American Opportunity Credit, Lifetime Learning Credit, or the Tuition and Fees Deduction. The software will choose the one that will provide you the biggest federal tax benefit, if you qualify for any of those benefits.