You cannot change it yet. Sometime in August the portal for banking information for the monthly CTC payments is supposed to be ready for people who need to change banking information.
See Manage Payments on this link from the IRS:
https://www.irs.gov/credits-deductions/advance-child-tax-credit-payments-in-2021
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
