how to display the first item in a dropdown

[debutant_ISC]

hello,
do you know how to display the first item in a dropdown
here is my code :

 
    {name:"r_customer_name", title:"<b><span style='color: orange'>Client </span></b>", editorType:"select",  optionDataSource:"cs_customers",  
    					changed: function(){
    						var CustomerName = CS_CustomersList.getValue("r_customer_name");
    						CS_CustomerID = CustomersResultSet.data.find({r_customer_name : CustomerName}).r_customer_idnum; 
    						CS_ServicesTreeGrid.setCriteria({r_service_fk_customer_idnum :CS_CustomerID }); 
    						CS_OrderViewList.fetchData({r_customer_idnum :CS_CustomerID }); 
    						NewCar_CustomerID = CS_CustomerID;
    					}
    }

there is a function

 selectRecord()

but it works only for listGrid