Display all sub category but one

If you’d like to exclude certain subcategories in a category archive page, try put the following code in your functions.php:

function exclude_category( $query ) {
    if ( $query->is_category( 'myslug' ) && $query->is_main_query() ) {
        $query->set( 'cat', '-1,-1347' ); //Add your excluded subcategories ids
    }
}
add_action( 'pre_get_posts', 'exclude_category' );

If it’s not the case, we need your code to see the whole picture.