You would be able to use a custom image or text instead of the default chat bubble by customising the widget code. You could refer to the sample widget code here, to replace the chat bubble with a text.

Alternatively, you could also hide the existing chat widget on your site using:

headerProperty: { hideChatButton: true } as part of config. Once the chat widget is hidden, you would be able to use the method, upon clicking any custom button or text on your website.