How to retrieve data from parent form to Child form

 private void btnAdd_Click(object sender, EventArgs e)

        {

            if (txtBookId.Text != null)

            {

                txtBookId.Enabled = true;

                DTPDate.Enabled = true;

                btnShowBookId.Enabled = true;

                txtQtyBefore.Enabled = true;

                txtQtyReceived.Enabled = true;

                txtQtyAfter.Enabled = true;

                txtOrderNum.Enabled = true;

                btnAdd.Text = "Save";

            }

            else if (btnAdd.Text=="Save")

            {

                try

                {

                    string MyConString = "SERVER=localhost;" + "DATABASE=bookshop;" + "UID=root;" + "PWD=password;";

                    MySqlConnection Con = new MySqlConnection(MyConString);

                    MySqlCommand Cmd = Con.CreateCommand();

                    string S = "Insert into bookinventory values('" + txtBookId.Text + "','" + DTPDate.Text + "'," + txtQtyBefore.Text + "," + txtQtyReceived.Text + "," + txtQtyAfter.Text + "," + txtOrderNum.Text + ")";

                    Cmd = new MySqlCommand(S, Con);

                    Con.Open();

                    Cmd.ExecuteNonQuery();

                    Con.Close();

                }

                catch (Exception ex)

                {

                    MessageBox.Show(ex.Message);

                }

                

            } 

  }
My requirements are when i click on add button the text on button has to change save and the when i click on save it has to save the details into database i.e bookinventory database.

i am using above code for that but it's not saving the data into database. just check and give me some solution

Thanks.