@blackwoodfamily Have you already printed and mailed your return? 

@DaraLO  I have neither printed nor mailed my return.  I finished the process and saved the PDF but did nothing else before making the changes.

If you have already e-filed your return, you will not be able to add additional information. You will have to amend the return. 

  To amend your 2019 tax return: Wait to see if your return has been accepted or rejected by the IRS or state. If rejected, you can correct and re-send your return. If accepted you should wait until your return has been processed and you receive your refund or conformation that any tax due has been paid. If you file an amended return while you first return is being processed it can cause extended delays for both returns if two returns are in the system at the same time. In addition, if the IRS makes any change on your original return, you might end up having to amend the amendment. Amended returns can only be mailed - allow 8-12 weeks - can take up to 16 weeks (4 months) for processing. Be sure to save a copy of your return before you begin to amend. 

How do I amend my 2019 TurboTax Online return? https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/00/27577

To Amend on Windows. https://turbotax.intuit.com/personal-taxes/cd-download/amend/ty19/