if your return has been accepted or mailed in you can't change the DD info. if it is invalid the IRS will send you a check.
if not use the Find tool to search for “direct”, select Direct Deposit for [Your Name] from the list and click Go. Choose Yes from the options and click Continue. Choose Print and mail return and click Continue. Then enter your direct deposit info, and click Continue to save it and move on.
You cannot change banking information for your tax refund after you file your tax return.
If you are asking about changing your banking information for the monthly child tax credit payments you do that on the IRS portal: