When creating a video set, the initial preview video will contain the default settings in your build.
You can change back to this preview at any time by pressing "Original video" above the preview window.
You can also preview your custom settings in the editor, such as changes to language, resolution or any gameplay variable.
Once your changes are applied, simply press the "Customised" button above the preview window & select the row that lists the changes you've made.
You can read more about previewing videos here.