How do I edit the free wp plugin "Search"

I have inserted the free wp plugin "Search" on my site at http://www.icbv.net and I need to be able to add a form label to the search input box. I can't find this plugin in the plugin list or in the advanced text editor so I do not know how to get at the html that generated the form field which is where I can modify the code to add a label to the form field. Please help.
Thanks,
Kathy