This is plugin that helps you to search and replace any post content. Put this file to wp-content/mu-plugins folder and edit as you wish. Refresh the page and delete file after you see "success" on page.

posts-search-replace.php

<?php
/*
Plugin Name: Posts Search Replace
Description: This plugin helps you to search and replace any post content.
Version: 0.1.0
Author: Oz
*/

$post_type      = "page"; //use page or post or any post type you created
$filter_type    = "include"; //use exclude or include
$filter_array   = array(); //add post ids

$search         = "Find this text"; //enter what you want to search.
$replace        = "Replace with this"; //enter what you want to replace.

function execute_search_replace(){
    global $post_type, $filter_type, $filter_array, $search, $replace;

    $args = array(
        'post_type' => $post_type,
        'posts_per_page' => -1,
    );

    if($filter_type == "exclude"){
        $args["post__not_in"] = $filter_array;
    } elseif ($filter_type == "include") {
        $args["post__in"] = $filter_array;
    }

    $srquery = new WP_Query($args);

    foreach ($srquery->get_posts() as $post) {
        $new_post_content = str_replace($search, $replace, $post->post_content);
        $post->post_content = $new_post_content;

        wp_update_post($post);
    }

    die(var_dump("success"));

}

add_action("init", function(){
    execute_search_replace();
});