Clearing text entry boxes in try it mode

Hello people

I've created some software simulation and all is good. However, I've added a retake button at the end and the course starts again but when it comes to the first text entry box it still has the old text the person wrote in it. It also seems to bring the player to a grinding halt and there is nothing I can do. Any ideas how to clear this text so a person can practice multiple time? I'm using restart course when the user clicks button. 

Any advice much appreciated.