Help selecting dynamic item from a drop down Panel

Hi,

I've a Drop Down Panel with large selection of items and each itmes has checkbox next to it, and user can check multiple selection. 

I'm trying to check the first item from the drop down list and this is dynamic Text. Object identifier and object type is the same. It's the object label that changes. i'm just not sure how do i use the index to create the first item from the list. any suggestion will help

Thanks