I have plus account for my client how to add text like "Powered by Client Company Name" at the bottom of the chatbot User Interface. Just like Build With IBM Watson.

  <script>
      window.watsonAssistantChatOptions = {
          integrationID: "5689411d-538c-44c2-87c5-f7dd2bc156be", // The ID of this integration.
          region: "us-south", // The region your integration is hosted in.
          serviceInstanceID: "f6c21fcb-341c-4546-aa96-1587230b3fec", // The ID of your service instance.
          openChatByDefault: true,
          onLoad: function(instance)
           {     
             instance.writeableElements.footerBottomElement.innerHTML = '&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp Powered By <a target="_blank" href="https://nbsincorp.com/" rel="noopener"><strong>Nexgen Business Solutionss</strong></a>';
             instance.render();
             }
        };
      setTimeout(function(){
        const t=document.createElement('script');
        t.src="https://web-chat.global.assistant.watson.appdomain.cloud/versions/" + (window.watsonAssistantChatOptions.clientVersion || 'latest') + "/WatsonAssistantChatEntry.js"
        document.head.appendChild(t);
      });
    </script>