'Code within >> button click event
For Each gridItem As DataGridItem In DataGrid1.Items
     Dim list1 As ListBox = CType(gridItem.FindControl("List1"), ListBox)
     Dim list2 As ListBox = CType(gridItem.FindControl("List2"), ListBox)
 
     For Each item As ListItem In list1.Items
          If item.Selected Then
               list2.Items.Add(item)
          End If
     Next
Next
 

//Javascript Code: 
//function should take an input of the current index
function SwapLists(idx) {
 
    var inpt = document.frmProdDetail.getElementsByTagName("input");
    var list1, list2;
 
    for (var i = 0; i < inpt.length; i++)
    {
 
        if (inpt[i].id.match('ctl' + idx + '_MyAspxListBox1') != null) {
            list1 = inpt[i];                 
        } else if (inpt[i].id.match('ctl' + idx + '_MyAspxListBox2') != null) {
            list2 = inpt[i];
        }
    }
 
    //Write your javascript to transfer selected items from list1 to list2
}