In the Data Feed settings, when you select "XML" for the Format, you will need to enter a value for Product Element.

The "Product Element" is basically the element in the XML file that contains the product data.

For Example:

In the above screenshot, the element that contains the product data is simply called Product, so that's all we need to enter in the Data Feed settings:

Please note that we don't support more complex XML data structures where data might be grouped or deeply nested.