How to prevent post to repeat on my loop?

Question

As mentioned in comment by @Michael,

offset does not work with 'posts_per_page' => -1

You can possibly use increment to make first slide as active, in a single loop.

Use this

<div class="carousel-inner" role="listbox">
    <?php $the_query = new WP_Query(array(
        'post_type' => 'Banners', 
        'posts_per_page' => -1 
    ));
    $i = 0;
    while ( $the_query->have_posts() ) : $the_query->the_post(); ?>
    <div class="carousel-item <?php if($i == 0) { echo 'active'; } ?>">
        <img class="img-fluid" src="https://wordpress.stackexchange.com/questions/263869/<?php the_field("banner-image'); ?>">
    </div>
    <?php $i++; ?>
    <?php endwhile; wp_reset_postdata(); ?>
</div>