Untitled

<p id="btnOne">Botao abrir</p>
<script>
    document.getElementById("btnOne").addEventListener("click", function() {



            const iframe = document.getElementById("cb-duotalk-chat-frame");
            if (iframe != null)
                iframe.contentWindow.postMessage(
                    { openChat: true, showCloseButton: true },
                    "*"
                );
        });

</script>