What do I need to do if I filed my federal tax return prior to finding out that the MCTR did not have to be included?

[JohnW152]

You can amend your return to remove this income, which may result in a refund. 

Please see the TurboTax Help article How to File an Amended Tax Return with the IRS for guidance.

You should wait to file your amended return until you get any refund you may have coming from your original return.  Even if your original return has been accepted by the IRS, it's still possible that the IRS could change your refund or balance due on that return.