search bar to serach by category

I need help with a search bar to search by category
I currently have a search bar functioning already but need one for the other category. We have two categories one called events and one called concerts
category for events has the category ID= 4709 the other category has the ID- 4713
we have the suggestion to hide one category and that should omit a category from being searched by the hidden input type.

The search bar currently is code as follows which searches the events below:

<div class="em-events-search"><form class="em-events-search-form" method="post" action="http://dev.bookmanstest.com/events/">
      <!-- START Category Search -->
    <p></p><select id="category" class="em-events-search-category" name="category"><option value="-1"></option><option class="level-0" value="4709"></option></select><p>
      <!-- END Category Search -->
    </br>
      <!-- START City Search -->
    </p><select class="em-events-search-town" name="town"><option value="">
      All Locations
    </option><option>
      Mesa
    </option><option>
      Phoenix
    </option><option>
      Tucson
    </option></select><p>
      <!-- END City Search -->
    </br><input type="hidden" value="search_events" name="action"></input></br><input class="em-events-search-submit" type="submit" value="Search"></input></br></p></form></div><p></p>

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Please help to search by the concerts category please the code above searches events

thanks