Finding Repeated Values in List String

Question

I want to check if there are repeated values in the List and if there are any then display print in a txt file

 List<String> Die_ID_refrence = new List<String>();
//List stores All Die_ID from t0 sheet
               for (int a = 0; a < table5.Rows.Count; a++)
           {
               Die_ID_refrence.Add(table5.Rows[a]["Die_ID"].ToString());
             
           }