Get content block by post ID

Hello,
I am trying to retrieve the content of a block via its ID.
I tried something like this

<?php             
             
                $post_id = 234;
                $post = get_post($post_id);
                $blocks = parse_blocks($post->post_content);
                print'<pre>';print_r($blocks);print'</pre>';
                            
                foreach ($blocks as $block) {
                    if ($block['image_header'] == 'lazyblock/client-header') {
                       render_block($block);
                    }
                }
            ?>

Array
(
    [0] => Array
        (
            [blockName] => lazyblock/client-header
            [attrs] => Array
                (
                    [titre] => Lorem ipsum
                    [header_image] => %7B%22alt%22:%22Gulf-Air%22,%22title%22:%22Gulf-Air%22,%22caption%22:%22%22,%22description%22:%22%22,%22id%22:359,%22link%22:%22//192.168.1.35:3000/fr/client/amiri-flight/gulf-air-5/%22,%22url%22:%22//192.168.1.35:3000/wp-content/uploads/2021/02/Gulf-Air-5-scaled.jpg%22,%22sizes%22:%7B%22thumbnail%22:%7B%22height%22:150,%22width%22:150,%22url%22:%22//192.168.1.35:3000/wp-content/uploads/2021/02/Gulf-Air-5-150x150.jpg%22,%22orientation%22:%22landscape%22%7D,%22medium%22:%7B%22height%22:300,%22width%22:200,%22url%22:%22//192.168.1.35:3000/wp-content/uploads/2021/02/Gulf-Air-5-200x300.jpg%22,%22orientation%22:%22portrait%22%7D,%22large%22:%7B%22height%22:960,%22width%22:640,%22url%22:%22//192.168.1.35:3000/wp-content/uploads/2021/02/Gulf-Air-5-683x1024.jpg%22,%22orientation%22:%22portrait%22%7D,%22full%22:%7B%22url%22:%22//192.168.1.35:3000/wp-content/uploads/2021/02/Gulf-Air-5-scaled.jpg%22,%22height%22:2560,%22width%22:1707,%22orientation%22:%22portrait%22%7D%7D%7D
                    [soustitre] => Lorem ipsum dolor
                    [blockId] => Z2gkChz
                    [blockUniqueClass] => lazyblock-client-header-Z2gkChz
                )

            [innerBlocks] => Array
                (
                )

            [innerHTML] => 
            [innerContent] => Array
                (
                )

        )

How to get the URL of header_image ?