Passing values in list to SQL server in c#

It's a little complicated, if you mean you want to INSERT them as different row values.
It's pretty simple to do from a DataTable - just use SqlBulkCopy.WriteToServer[^] but there is no equivelant for a List<T>.
However, you could use this: Converting a List to a DataTable[^] or just use a DataTable to start with.

Why not simply loop the collection and insert the row on each loop. Something like

using (System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection()) {
   try {
      connection.ConnectionString = connectionString;
      connection.Open();

      sql = "INSERT INTO MyTable (MyColumn) VALUES (@value)";
      using (System.Data.SqlClient.SqlCommand command = new System.Data.SqlClient.SqlCommand(sql, connection)) {
         command.Parameters.Add(new System.Data.SqlClient.SqlParameter("@value", 
                                         System.Data.SqlDbType.Int));
         command.Prepare();

         foreach (int value in iList) {
            command.Parameters["@value"].Value = value;
            command.ExecuteNonQuery();
         }
      }
...