Assign a chatbot after a rule

To be able to set a rule that if the message is something like...  “I saw this on Facebook” to assign the user to the chatbot.  Typically our users have 5-10 typical questions that the chatbot can answer.  I don’t want to use the flowbot because it would mean I’d have to create 10 choices – in my experiments I can say that users never type in the input area if they are presented options from the flowbot, even if the choices make no sense.