Copy Textbox Value from form to subform textbox

[James]

I have been working on a form that has a subform
displaying data from a query. I would like to click a
button and transfer the SSN on the main form to a selected
record in the subform.
I've used code to do the event procedure on a button on
the subform, only I do not know how to ID the main form in
the code to tell it where to pull the value from.

SSN.text = Text14.text

How do I code Text14's location on the main form?

Thanks!