Use Select Element - this will allow you to select which element to interrogate. You can then select the inner table. Adjust the match rules to make it unique and then you should be able to right-click and choose Design Table.
You can't really add the column names as part of one table when they are actually part of another. You'll need to deal with the data portion of the table separate from the headers. It would be interrogated as its own object in the hierarchy.