I have another way for you to accomplish this in QuickBooks Online, Irincker.
At the moment, importing a customer list with account numbers isn't an option. You'll want to import the customer list first and manually enter the account number after. Alternatively, you can also use a third-party application that lets you import both sets of information. To search, type in a keyword on the search bar. Attached is a screenshot for your reference:
![](https://lithium-response-prod.s3.us-west-2.amazonaws.com/intuit.response.lithium.com/RESPONSEIMAGE/c694fb53-320e-4220-9671-5fe7df705403.default.PNG)
Furthermore, after you're able to successfully import customer information, learn how to run reports and customize them to get the data you need most. I've added this article for more information: Customize Reports in QuickBooks Online.
Let us know if you have any questions about importing the customer list and account numbers. We're always here to assist you further. Have a great day ahead.