You cannot amend until your original return has been fully processed. After it has been processed you can prepare a Form 1040X to amend. You delete a dependent in My Info. Meanwhile, if there is someone else whose return is being rejected because you claimed the child, they have to file by mail. Waiting for you to amend will not help them. The only way they can file and claim that child is by filing a paper return and mailing it.
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