At the moment we can only customise sales forms like your invoices, quotes and sales receipts in QuickBooks Online. The customer statements cannot be customized and follows the default layout in the system.
It would be great if you could drop your feedback within the QuickBooks feedback tool so it will then be forwarded to our product team for review. Click on the Settings icon in your QBO account, and click on Feedback.
You can check these link to learn more about statements and customising sales forms: