Go to the following link for instructions to amend a 2019 tax return that you filed with TurboTax Online.
How do I amend my 2019 TurboTax Online return?
An amended return has to be filed on a special form, Form 1040-X. It cannot be e-filed. You have to print it, sign it, and file it by mail. It takes the IRS up to 16 weeks to process an amended return.
Don't file the amended return until your first return has been accepted and you have received the original refund.