You need to wait until you hear if your already-efiled return is accepted or rejected by the IRS. While you may have to ultimately amend, you might luck out if the IRS rejects your return.
If rejected, that's the easiest to fix. You just make the correction, add any additional form, etc. and resubmit the efile.
It accepted, however, then the only way to correct is with a formal amended tax return Form 1040X.
Unfortunately, due to late tax law changes the IRS will not even open up to start processing until February 12, 2021, except for a few returns they pull early for testing purposes. In the meantime the return will sit on TurboTax servers with a "pending" status but cannot be retrieved to cancel or correct. So unless yours is one of the very few returns pulled early by the IRS, you won't know anything until February 12 or soon thereafter.
So in the meantime do NOT make any changes in your return until you find out if it's accepted or rejected by the IRS. If you end up having to prepare an amended return, it has to start out exactly as it was when originally filed.
