Not able to set Data source in teststep

Hi,

I am still new to soap ui pro. I was trying a http test where I add a new contact and get the id of the contact. Adding contact works. But how do I get the id of that contact from the http response? When I try to setup a datasource in the next test step, I am not able to set it. When I select "Excel" or "File" from the drop down, it is not selected. Is this a known issue? Is there a work around? Please let me know.

Thanks!