Force all to select the same template?

Hi

When I look at this:
https://premium.wpmudev.org/blog/how-to-set-the-default-theme-for-wordpress-multisite/
I need to setup an template blog and that are done.

But how to I force all to select the same template?
https://simplylearn.no/wp-admin/network/admin.php?page=blog_templates_settings