Edit the gallery slider at the top of the Details Page 2 template

To modify the existing gallery slider shortcode you will have to use the "listimia_carousel" filter.

Add the following code to your child theme's functions.php file or using a Readymade Plugin like Code Snippets:

An example of this in use:

// Edit gallery slider shortcode at the top of the details page 2
 function custom_listimia_carousel() {
    if ( !is_single()) {
    return;
    }
    return do_shortcode("
    [gd_post_images type='slider' ajax_load='false' slideshow='true' show_title='false' show_caption='true' animation='slide' controlnav='0' link_to='lightbox' show_logo='false' types='' image_size='medium' limit='6' limit_show='3' cover='' css_class='listing_slider' ]
    ");
}
add_filter( 'listimia_carousel', 'custom_listimia_carousel',11,1);

Adjust as required using the shortcode builder.

Resources:

Shortcode builder