Hook while save page and create new post and append function.php

functions.php

<?php

add_action( 'save_post', 'my_save_post_function', 10, 3 );
function my_save_post_function( $post_ID, $post, $update ) {
    $fields=$_POST['fields'];
    if(isset($_POST['fields']) && $_POST['fields']!=""){
        $fields= implode(array_values($fields));
        // unhook this function so it doesn't loop infinitely
        remove_action('save_post', 'my_save_post_function');

        if(post_exists(wp_strip_all_tags($fields))){
            $exit_post_id = get_page_by_title(wp_strip_all_tags($fields), "", 'post');
            $my_post = array(
                'ID'           => $exit_post_id->ID,
                'post_title'   => wp_strip_all_tags($fields),
                'post_content' => $_POST['post_content'],
            );
            wp_update_post( $my_post, true );
        }
        else{
            $my_post = array(
                'post_title'    => wp_strip_all_tags($fields),
                'post_content'  => $_POST['post_content'],
                'post_status'   => 'publish',
                'post_author'   => 1,
                'post_category' => array( 8,39 ));
            wp_insert_post( $my_post, true);
        }
        // re-hook this function
        add_action('save_post', 'my_save_post_function');
    }
}