Yes, you can amend if the prior tax return was incorrect.

https://proconnect.intuit.com/community/amend-tax-return/help/how-do-i-amend-an-individual-return-us...

Changing that box should allow the full amount of the Child Tax Credit to be refundable.

However, I don't think that has anything to do with the Recovery Rebate Credit.  Why do you think that is affected?

Did the IRS change something else on the tax return, or did they only change something in relation to the Child Tax Credit and/or the Recovery Rebate Credit?