How to edit Search Results page?

but isn’t it the default behavior that search results page got a sidebar?

you can manage the position by that snippet:
(if you like a sidebar left … you know what to change?)

function avia_change_layout_for_searchresults($layout, $post_id) {
    if( is_search() ) {
        $layout['current'] = $layout['sidebar_right'];
        $layout['current']['main'] = 'sidebar_right';
    }
    return $layout;
}
add_filter('avia_layout_filter', 'avia_change_layout_for_searchresults', 10, 2);

if you like to show a custom sidebar on that page you can do it via:

add_filter("avf_custom_sidebar", function($custom_sidebar) {
    if( is_search() ) {
        $custom_sidebar = "Your Custom Sidebar Name"; 
    }
    return $custom_sidebar;
}, 10, 1);