Forcing intent recognition

I am currently trying to use an intent classification with a text box for an untrained intent. The idea behind it is to use a text box in a form. The user is requested to insert the value for the intent into the box. Now the question is, how can the chatbot recognize in that form that the content of the text box is the answer and puts the content into the slot. With the slot filled the form can move on. Has anybody done something like this or has an idea?