First, look at your tax return Form 1040 Line 30 to see if there is a Recovery Rebate Credit of $1,400 entered.
If there is an entry then the child's $1,400 credit was included in your tax return. If there is no credit, then you will have to amend your 2021 tax return to receive the Recovery Rebate Credit for the child.
An amended return, Form 1040-X, can only be printed and mailed to the IRS if the original tax return was not e-filed. The IRS will take up to 16 weeks or longer to process an amended tax return.
See this TurboTax support FAQ for amending a 2021 return - https://ttlc.intuit.com/community/tax-return/help/how-do-i-amend-my-2021-return/00/2544441
