Repeated Grid configuration issue

I have used the repeated grid. I want to populate the data list in the orbeon form. But, I don't know how to bind the data into Orbeon form builder. Can you please give me the example or suggestion?

For Example: I have mapped firstName text box in Repeated grid in Orbeon form. I have wrritten the formData.put("firstName", keyPerson.getFirstName()); line in for loop. because it was collection. Now How can i mapped the firstName in Form builder Advanced tab-->Actions tab? Please, can anyone give me the example or graphical presentation about this issue. Please give me the vedio link if any. Please find the attachment. What should be the entry or configuration in Action tab in form builder of Orbeon?