Warm greetings, lscovil-aquickpi. I see the benefits of being able to modify your customers' statement template.
The option to change the customer statement template in QuickBooks Online is currently unavailable. Nonetheless, you can select to list each transaction as a single line, including all details, and show the aging table at the bottom of the form.
If you wish to change this, here's how:
Hover over the Gear icon and select Account and settings.
Click the Sales menu, then press the Statements section to open it.
Choose the option you want (List each transaction as a single line, List each transaction including all detail lines, or Show the aging table at bottom of statement.
Hit Save.
I've included a screenshot for visual reference.
There are various types of customer statements in QuickBooks Online. If you want to know more about them, please check out this article: Create and view customer statements.
Moreover, I'll add these articles to guide you in generating reports in QuickBooks that will let you see your customers' balances and sales summaries.
Whenever you need further clarification and information concerning customers' statements, I'm always here to help you. You can click the reply button below and enter your queries.