How to make cheked some items on SelectItem multiple

Hello,

I have a select item in my dinamicform with a listgrid into with data, I already solved to saving multiple items to my database, but now what I want is to recover this multiple items checked in my selectitem, I was looking for the "getrecords of the selectitems" but I coudn't find it , in order to compare, I would like to know is there some property of the select item to say that this item should be cheked? or something like this?

Any help please