Dynamic content block - how to create drop down

[anfield]

I have a dynamic content block (which is working now), with a free type string field. I'm wondering how can i create a drop down to select from so that the data can be filtered that way? The code is below Thanks

<?xml version="1.0" encoding="utf-8" ?>
<j:jelly trim="false" xmlns:j="jelly:core" xmlns:g="glide" xmlns:j2="null" xmlns:g2="null">
 
	
	  <style>	  		  

</style>
	
 <script>
	 
     var my_dashboardMessageHandler = new DashboardMessageHandler("FilterSubCategory");
    
    function publishFilter (searchTerm) {
        var filter_message = {};
        filter_message.id = "FilterSubCategory";
        filter_message.table = "dmn_demand";
	 
	 if (searchTerm == ""){
	 clearFilter();
	 } 
	 else {
	 filter_message.filter = "u_program_subcategorySTARTSWITH"+ searchTerm;
	 }
        SNC.canvas.interactiveFilters.setDefaultValue({
                id: filter_message.id,
                filters: [filter_message]
            }, false);
        my_dashboardMessageHandler.publishFilter(filter_message.table, filter_message.filter);
    }
    
    function clearFilter() {
        var filter_message = {};
        filter_message.id = "FilterSubCategory";
        filter_message.table = "dmn_demand";
        filter_message.filter = "";
        SNC.canvas.interactiveFilters.setDefaultValue({
                id: filter_message.id,
                filters: [filter_message]
            }, false);
        my_dashboardMessageHandler.removeFilter();
    }
 </script>   
	
            <input id="searchTerm" type="text" class="form-control" value="" onchange="publishFilter(this.value);"></input>
   
</j:jelly>