add_action('init','all_user_update');


function all_user_update()

{
	$wp_user_query = new WP_User_Query( array( 'role' => 'administrator' ) );
	// Get the users
	$users = $wp_user_query->get_results();
	$users = get_users( [ 'role__in' => [ 'author', 'subscriber' ] ] );
	 $users = $wpdb->get_results("SELECT ID, display_name FROM $wpdb->users ORDER BY ID");

	// Check for users
	if (!empty($users))
	{
	// Loop through each user
		//$i=0;
	for ($i = 0; $i <= 600; $i++) {
		foreach ($users as $user)
		{
			//$i++;
			// Add the meta_key and the value
			 add_user_meta( $user->ID, '_new_user', '1');
			 delete_user_meta( $user->ID, '_new_user', '1');
			//if($i==600) break;


		// Add the meta_key and the value
			 //delete_user_meta( $user->ID, '_new_user', '1');
			//add_user_meta($user->ID, 'name_of_new_meta_key', 'value_of_meta_key', false);
		}
	}
	} else {
	echo 'No users found.';
	}

}