You would simply pass that input node in as the user input for them as if they were at that point in a conversation.
For nlc specifically, the way I see it is that you would likely want your classes to match your input nodes so that when passing you do not need to do any manipulation in between.
User: open an account
Class = open account
Input: open account
Note that you will need to initialize a conversation first so you have a conversation and client id, from there it's a simple as passing it in as the users input with the API call.
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