How to set up the initial value for Data Iterator

Hey I am wondering if there is a way to set up the initial value for a Data Iterator? I see the properties have a “Start Index” field, I have been trying to use it but to no effect.

What I am trying to do?
So rather than having a page where users can go from one record to the next, I want to do this in a modal window.
The information in the modal window is selected from a table that has all the records, now when the modal window opens, I would like users to have the ability to move from the current record to the next or previous. (I got the part where users can move from one record to the next one). However, when the modal window first opens, it uses a different record than the one that was selected.
Hope someone can help
Regards
J