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You can use the Update/Calculate Field condition in order to duplicate the result of one field to another. Here's a guide: How-to-Pass-Field-Value-to-Another-Field.
I created 2 Text Boxes, the Original and the Duplicate field. After that, I created a condition wherein if the Original text box is filled, then the value will be copied to the Duplicate field.
Here's the result:
Hope that helps. Thank you.