<?php
$posts = $wp_query->posts; // Gets all post data from the main query

$c = []; // Going to hold an array of new keys for later use
if ( have_posts() ) {
    $count = 0; //Start the counter
    $ppp = get_option('posts_per_page'); // Gets the backend posts per page option set. Will be used in conjustion with the counter

    while ( have_posts() ) {
        the_post();
            if(has_tag('test')) { // This will be the tag to test against, your desired tag
                $c[] = $count++;
            }else{
                $c[] = $ppp + $count++; // Adds posts per page value to each count to advance posts without desired tag past desired tag
            }
    }
}
$posts_reordered = array_combine( $c, $posts ); // Reset each post from main query's key with the new keys created by $c
$sort_posts = ksort($posts_reordered); // Sort the new array according to key
/* ?><pre><?php var_dump($posts_reordered); ?></pre><?php   */ // Uncomment to dump your array to get objects

foreach ($posts_reordered as $value) {
    echo '<h1>' . $value->post_title . '</h1>';//This will be your new loop
    echo get_the_post_thumbnail( $value->ID);
    echo apply_filters( 'the_content', $value->post_content );
}
?>