Yes, you have to file an amended return to make the correction. Go to the following link for instructions to amend a 2018 tax return that you filed with TurboTax Online.
https://ttlc.intuit.com/questions/4667226-how-do-i-amend-my-2018-turbotax-online-return
An amended return has to be filed on a special form, Form 1040X. 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.
