You've come to the right place, Michael_Vowles.

Importing a sub-account is not possible in QuickBooks Online. Simply add it in the Account Name column in this format: Main account: sub-account.

For example, Utilities: Telephone. I've added a screenshot below to see an example of how to format a sub-account.

You may also use this article to learn how to upload the spreadsheet and map fields: Import your chart of accounts to QuickBooks Online.

In addition to this, if you need to connect the sub-account, please know first how the bank sends the downloaded transactions. This article will share more information about connecting account to Online Banking: About bank or credit card subaccount setup.

Get back to me if you have additional questions about this by commenting below. It's always my pleasure to help you. Take the best care always and have a wonderful weekend!