Good to see you in this thread, oceanbeachesglass.

At this time, you can only customize sales forms, like invoices, sale receipts, and estimates in QuickBooks Online. You may consider looking for a third-party application that offers a customizable purchase order.
 

You'll want to click the Apps menu on the left navigation bar. Then, you can click on the Browser category drop-down list, and use filters to narrow down your search.

Also, I've added articles to learn more about how P.O works in QBO:

• Create and send purchase orders in QuickBooks Online.
• What is the quantity on purchase order (PO)?

Feel free to reach out back to me if you need anything else about customizing templates in QBO.