I can help update your personal checking account number in QuickBooks.
If you mean the bank account for QuickBooks Payments, you can update the information through your settings. I'll show you the steps on how to do it below:
Sign in to QuickBooks Online in a web browser.
Click the Gear icon, then select Account and settings.
Go to the Payments tab.
In the Deposits section, next to Standard Deposits, select Change bank.
Select Add new bank account.
Enter the routing number and account number of the bank account you want to change to.
Select Save when you're ready.
Review the bank account info and make sure it’s selected before completing your request.
If you mean the account number of your checking's account added under the chart of accounts, you can follow these steps:
Click the Gear icon in the upper-right corner.
Select Chartof accounts under Your Company.
Search for the account.
Press the drop-down arrow next to View register.
Choose Edit.
Update the account number.
Hit Save and Close.
In case you're referring to something else, please let me know. You can add more details by leaving a comment.