Move Data from Multi Line to other Multi or Single Line

Move Data from Multi Line to other Multi or Single Line

Hi, i am try to move a data from multi selectin box to a single or multi line. i can do that with single to single but problem is transfering froma multi line. i try to use this simple code as below; 

  2. if(servis_personeller == null)
  3. {
  4. input.servisPersonel_Deluge = "";
  5. }
  6. else
  7. {
  8. x = Bakim_Personel_Formu[ID == input.servis_personeller];
  9. y = x.personel_adsoyad;
  10. input.servisPersonel_Deluge = y;
  11. }
But it only move last selection. i want to move all selection Like ; AAA,BBB,CCC
Please advise. Thanks.