Hello, accounting-petty.
I'll help you change the vendor information to modify the routing number. You'll need to open any bills or bill payments to your vendor and select the Schedule online payment. I'll show you how to do it:
- Go to Expenses.
- Select Vendors at the top.
- Click the Schedule payments under Action.
- Press the Settings at the top of the screen.
- Select the vendor you need to change the banking info.
- From there you can change the routing and account numbers.
- Hit Save once done.

You can read more about the online bill pay feature in QBO through the following articles:
Please keep in touch with me here should you need any further assistance regarding updating the bank account info. The Community always has your back.