WordPress Tutorial: In simple steps, going to show you how to add a search bar in the WordPress main menu. The following codes are tested by using WordPress Child Theme.
Step 1: Open functions.php file from the child theme.
Step 2: Add this below code
/*==========================================
Adding Search Box in Main Menu
===========================================*/
add_filter( 'wp_nav_menu_items', 'main_nav_search', 10, 2 );
function main_nav_search($items, $args){
// if this isn't the primary menu, do nothing
if( !( $args->theme_location == 'primary' ) )
return $items;
// Otherwise, add search form
return $items . '<li>' . get_search_form(false) . '</li>';
}
Step 3: Save it and you are done.