Difficulty in interacting with an existing node

I’m trying to ask follow up questions with the same node, however every time I try (eg. click on the node or move the new branch icon underneath the conversation box) it will always generate a brand new chat. I have no luck to command the existing node for further actions. Also when I click the new branch icon there will be a chat box to ask for my input, but no matter what I type and enter, there won’t be any response. Any advice or tutorial please, many thanks!!