This page redirects to an external site: https://developer.wordpress.org/reference/classes/wp_customize_manager/get_section/
Use like$wp_customize->get_section( 'header_image' )->description = __( 'Applied to the header on small screens and the sidebar on wide screens.', 'twentyfifteen' );