To set the order layout, click on the ‘Setup’ button and you will be redirected to the Setup page.
From setup page, navigate to Build -> Customize -> Order -> Page Layouts.
By clicking on the ‘Page Layouts’ link, you will be redirected to the Order Page Layout page.
Now click on the ‘Edit’ button beside ‘Order Layout’ to edit that layout.
Now drag the ‘Related Contact’ field to the Order Detail section and click on the ‘Save’ button to save the changes.