how i can insert data in table has a foreign key in its column ?

public string storeText_intoDB(string str )
{
    using (SqlConnection conn = new SqlConnection("Data Source=TOSHIBA-PC\\SQLEXPRESS;" +
    "Initial Catalog=FileDB;Integrated Security=True;Pooling=False"))
    {
        try
        {
            conn.Open();
            //SELECT MAX(column_name) FROM table_name
            string strsql = " select MAX( FileID )from File_Table  ";
            SqlCommand cmd1 = new SqlCommand(strsql, conn);
            object result = cmd1.ExecuteScalar();

            if (result == null)
            {

                return "Error IN FileID";
            }
            else
            {
                SqlDataReader myreader;
                myreader = cmd1.ExecuteReader();

                while (myreader.Read())
                {
                    SqlCommand cmd = new SqlCommand();
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.CommandText = "StoredProcedure1";
                    cmd.Connection = conn;

                    cmd.Parameters.AddWithValue("@FileID", myreader["FileID"]);

                    cmd.Parameters.AddWithValue("@ttext", str);
                    cmd.ExecuteNonQuery();
                    MessageBox.Show("Texts STORED successfully");
                    return "text stored Successfully!!!";
                }
                MessageBox.Show("Texts don't STORED successfully");
                return "My reader not working in text stored !";


            }
        }
        catch (Exception ex)
        {
            return ex.Message;
        }
            finally
            {
                conn.Close();

                conn.Dispose();

            }
        }



        }