function blog_scripts() {
    // Register the script
    wp_register_script( 'custom-script', get_stylesheet_directory_uri(). '/js/custom.js', array('jquery'), false, true );

    // Localize the script with new data
    $script_data_array = array(
        'ajaxurl' => admin_url( 'admin-ajax.php' ),
        'security' => wp_create_nonce( 'load_more_posts' ),
    );
    wp_localize_script( 'custom-script', 'blog', $script_data_array );

    // Enqueued script with localized data.
    wp_enqueue_script( 'custom-script' );
}
add_action( 'wp_enqueue_scripts', 'blog_scripts' );


function load_posts_by_ajax_callback() {
    check_ajax_referer('load_more_posts', 'security');
    $paged = $_POST['page'];
    $args = array(
        'post_type' => 'reviews',
        'post_status' => 'publish',
        'posts_per_page' => '4',
        'paged' => $paged,
    );
    $my_posts = new WP_Query( $args );
    ?>

    <?php if ( $my_posts->have_posts() ) : ?>
        <?php while ( $my_posts->have_posts() ) : $my_posts->the_post(); ?>
        <div class="col-12 reviews">
            <div class="firstrw">
                <div class="foto-wrap">
                    <?php the_post_thumbnail();?>
                    <div class="firstrw_content">
                        <h1><?php the_title();?></h1>
                        <p id="data"><?php echo get_the_date( 'd-m-Y' ); ?></p>
                    </div>
                </div>
                <div class="star-rating">
                    <p><?php the_field('stars');?></p>
                </div>
            </div>

            <?php the_content();?>
            <hr>
        </div>
        <?php endwhile; ?>
        <?php
    endif;

    wp_die();
}
add_action('wp_ajax_load_posts_by_ajax', 'load_posts_by_ajax_callback');
add_action('wp_ajax_nopriv_load_posts_by_ajax', 'load_posts_by_ajax_callback');



///JS
var page = 2;
jQuery(function($) {
    $('body').on('click', '.loadmore', function() {
        var data = {
            'action': 'load_posts_by_ajax',
            'page': page,
            'security': blog.security
        };

        $.post(blog.ajaxurl, data, function(response) {
            if(response != '') {
                $('.reviews').append(response);
                page++;
            } else {
                $('.loadmore').hide();
            }
        });
    });
});
////HTML


<div class="container">
    <div class="row">
        <?php
        $args = array(
       'post_type' => 'reviews',
       'post_status' => 'publish',
        'posts_per_page' => '3',
        'paged' => 1,
         );
         $loop = new WP_Query($args);
         while ($loop->have_posts()) :
         $loop->the_post();
         ?>

        <div class="col-12 reviews">
            <div class="firstrw">
                <div class="foto-wrap">
                    <?php the_post_thumbnail();?>
                    <div class="firstrw_content">
                        <h1><?php the_title();?></h1>
                        <p id="data"><?php echo get_the_date( 'd-m-Y' ); ?></p>
                    </div>
                </div>
                <div class="star-rating">
                    <p><?php the_field('stars');?></p>
                </div>
            </div>

            <?php the_content();?>
            <hr>
        </div>



        <?php
           endwhile;
           wp_reset_postdata();
       ?>
       <div class="loadmore">Load More...</div>
    </div>
</div>
</div>
</div>