//$customer is https://woocommerce.github.io/code-reference/classes/WC-Customer.html
add_filter( "woocommerce_json_search_found_customers", function($results){
foreach($results as $id=>$result) {
    if($result["type"] == "customer") {
        $customer = new WC_Customer($result["id"]);
        if( $customer )
            $results[$id]["title"] = $customer->get_id() ." - " . $customer->get_billing_company();  //EDIT
    }
}
return $results;
},20 );