How do I parse values to text boxes from a row of selected cell in a datagridview in a windows forms app?

Question

I would like to know how to select a category value from a combo box and the data according to the selection parses to a data grid view from a sql database, after that I want to click on a cell and the data on that cell row must parse to text boxes in the form and I need to make changes to the record and update the record or delete it from the database. I've tried the following code but I keep getting errors.

private void dataGridView_StaffDetails_CellClick(object sender, DataGridViewCellEventArgs e)
{
    string staffType = comboBox_Type.SelectedItem.ToString();
    if (comboBox_Type.SelectedIndex != -1)
    {
        comboBox_Type.SelectedItem.ToString();

    }
    else
    {
        Btn_Search.Enabled = false;
    }

    //---SQL Command to Select Data
    try
    {
        //---Open Connection
        connection.Open();

        //---SQL Command to Select Data
        SqlCommand cmd = new SqlCommand("Select * from StaffDetails where Staff_Type = '"      + staffType + "' ", connection);

        //---Execute SQL Command
        SqlDataReader reader = cmd.ExecuteReader();
        if (reader.HasRows)
        {
            //---Read Data and assign to text boxes, radio buttons and combo box
            while (reader.Read())
            {
                Txt_FirstName.Text = reader["Customer_FirstName"].ToString();
                Txt_LastName.Text = reader["Customer_LastName"].ToString();
                Txt_Username.Text = reader["Username"].ToString();
                Txt_Password.Text = reader["Password"].ToString();
                Txt_SalaryPerMonth.Text = reader["Salary_Per_Month"].ToString();
                
                string StaffType = reader["Staff_Type"].ToString();
                comboBox_Type.SelectedItem = staffType;

                Btn_Update.Enabled = true;
                Btn_Delete.Enabled = true;

            }
        }
        else
        {
            MessageBox.Show("Sorry! No record was found ");
        }
        connection.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error: " + ex);
        connection.Close();
    }


}