I'd be glad to help guide you so you'll be able to connect your bank account to QuickBooks Online (QBO) successfully.
To connect your bank account:
Go to Banking at the left pane.
Select Add account.
Search for your bank.
Select the type of account you’re adding (savings, checking, or credit card).If you’re new to QuickBooks or don’t see the option you need in the drop-down, select + Add New to create a new account on your chart of accounts.
Select how far back you want to download transactions.
For additional reference, you may check these articles: