Adsense or banner below more tag

How are you adding that ad currently?

Another user finds this plugin very helpful: https://en-ca.wordpress.org/plugins/ad-inserter/

I use a Bannerplugin and Added a php code in the archive.php

<?php /* Start the Loop */ ?>
			<?php while ( have_posts() ) : the_post(); ?>

				<?php
					/* Include the Post-Format-specific template for the content.
					 * If you want to override this in a child theme, then include a file
					 * called content-___.php (where ___ is the Post Format name) and that will be used instead.
					 */
					get_template_part( 'content', get_post_format() );
				?>
------>		<?php if (!$show_adsense) { ?>
		<?php if(function_exists('drawAdsPlace')) drawAdsPlace(array('id' => 6), true); ?>
		<?php $show_adsense = 1; } ?> <------

			<?php endwhile; ?>

but i want this banner directly under the "more tag"

Editing core files is never good.

Instead, you could try using a filter:

add_filter( 'excerpt_more','tu_add_to_excerpt_more' );
function tu_add_to_excerpt_more( $more ) {
    return $more . '<div class="your-ad">AD HTML</div>';
}