For you to do, the IRS will adjust the return appropriately. This can delay your return a bit. If for any reason they failed to make the adjustment you can amend the return later after receive the original refund.
If your return has been accepted you will have to wait and see if your refund includes the additional credit. If yes then you will need to amend your return (1040X) and send the funds back to the IRS. Please see FAQ How to amend a tax return for instructions.
Please see IRS Recovery Rebate Credit Q D2 What happens if I claim the incorrect amount? for additional information.
Please see the links below when Form 1040X is available:
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