Import export – Drupal 8 + Modify the data structure of a REST view export

I need to create a sitemap.xml with a REST export in the views.
By default, I obtain this data structure with a REST export:


How can I modify the labels of this structure? I need to get these labels:


These labels must be changed:

    > <urlset ...

Do I write a custom serializer for the REST export? a specific encoder? If so, how to proceed?

Thanks for your help.