search-filter.php

<?php
function custom_search_query( $query ) {
	if( is_admin() && $query->is_main_query() && $query->query['post_type'] === 'revendeurs' && isset($query->query_vars['s']) )
	{
		$custom_fields = array(
			// put all the meta fields you want to search for here
			"raison_sociale",
		);
		$searchterm = $query->query_vars['s'];

		// we have to remove the "s" parameter from the query, because it will prevent the posts from being found
		$query->query_vars['s'] = "";
		

		if ($searchterm != "") {
			$meta_query = array('relation' => 'OR');
			foreach($custom_fields as $cf) {
				array_push($meta_query, array(
					'key' => $cf,
					'value' => $searchterm,
					'compare' => 'LIKE'
				));
			}
			$query->set("meta_query", $meta_query);
		};
	}
}
add_action( "pre_get_posts", "custom_search_query");