I’m not entirely certain that I understand your question. Are you asking how to have the chatbot “make the first move”, and issue an initial greeting to the user when they first load the web page? If so, that’s as simple as populating the web page with the initial greeting into the HTML element where the user would normally see the chatbot’s response. Once the user sends input, and program O returns a response, that initial greeting would then be replaced by the returned response. You can see an example of this with my chatbot, Morti.
Of course, if that’s not what you meant, then some further explanation on your part is necessary before I can give you a usable answer.