If you find something wrong on the Turbo Tax return you filed you can mail in an Amended return. You cannot change or add anything on the return that you e-filed. It is too late, just like when you put an envelope in a US mailbox
Now you have to wait until the IRS either rejects or accepts your return. If your return is rejected, you will be able to go into your account and add or change it and resend it.
If the IRS accepts your return, then you have to wait until it has been fully processed and you have received your refund. THEN you can prepare an amended tax return 1040X and mail it in. You cannot e-file an amended return. Meanwhile, DO NOT change anything on your return until you start the amended return.
The 1040X form for 2018 hasn't been approved yet by IRS. Please, keep checking the following information on how to amend your return; it will be updated once the 2018 form is released. How to amend an Online return
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