How to do a Change Order QB Desktop Pro 2019?

Hi there, @christy18.

You'll want to create a copy of the Sales Order or Purchase Order and make some changes from there. This way, QuickBooks will have a copy of the original order as well as the change order. Let me show you how.

In your QuickBooks Desktop (QBDT), to change a sales order:

1. Go to the Customers menu.
2. Select the Customer Center.
3. Locate the customer and select the Sales Order.
4. Click Create a Copy. 
5. Make some changes and click Save & Close once done.

For purchase order:

1. Go to the Vendors menu.
2. Click the Vendor Center.
3. Locate the vendor and click the Purchase Order.
4. Click Create a Copy. 
5. Make some changes and click Save & Close once done.

I also got you this article for reference in case you need to remove a credit form an invoice: Remove or unapply a credit from an invoice or bill.

I'd be around if you have more questions or concerns in the future. Take care!