Order Completed Screen

I'm certain I'm simply overlooking this in the configurations, but where can I customize the order completed screen?  JD uses this screen:
 

Hi Brian

You can just go to Documents Seller -> Messages, find the two message items:

- Thank You Message
- Thank You Message (Offline Payment) . For this one, you only need to change if you are using offline payment method

And change it to meet your need

Regards,

Tuan