It isn't very clear from your question exactly what you are trying to do. I am going to assume that you want the selected items from a populated listbox to be inserted into an empty listbox. Once it is stated that way, the answer should be somewhat obvious.

sub singleItemSelect{
  my  @selectedItemIndex = $lbl->curselection;
  for (@selectedItemIndex)
  {
     $lbr->insert('end', $lbl->get($_));
  }
}
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