I want to be able to select an option from a drop down and then display a grid with checkbox option and save the selected options in a database

public partial class ModView : System.Web.UI.Page
{
    SqlConnection con = new SqlConnection(@"Data Source=(localdb)\v11.0;Initial Catalog=facultylog;Integrated Security=True");
    protected void Page_Load(object sender, EventArgs e)
    {
        {

            String strConnString = ConfigurationManager.ConnectionStrings["facultylogConnectionString"].ConnectionString;
            String strQuery = "select Subject_Name from subjects";
            SqlConnection con = new SqlConnection(strConnString);
            SqlCommand cmd = new SqlCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = strQuery;
            cmd.Connection = con;
            try
            {
                con.Open();
                DropDownList1.DataSource = cmd.ExecuteReader();
                DropDownList1.DataTextField = "Subject_Name";

                DropDownList1.DataBind();
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                con.Close();
                con.Dispose();
            }
        }
        
        if (!Page.IsPostBack)
        {
            
          refreshdata();
        }

    }

 

    public void refreshdata()
    {
        SqlCommand cmd = new SqlCommand("select CourseOutcomes from CLO", con);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        sda.Fill(dt);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
   

    
    protected void Button1_Click(object sender, EventArgs e)
    {
        foreach (GridViewRow gvrow in GridView1.Rows)
        {
            var checkbox = gvrow.FindControl("CheckBox1") as CheckBox;
            if (checkbox.Checked)
            {
                var lblId = gvrow.FindControl("Label1") as Label;
                var lblSubjectName = gvrow.FindControl("Label2") as Label;
                var lblCourseOutcomes = gvrow.FindControl("Label3") as Label;


                SqlCommand cmd = new SqlCommand("insert into savedCLO (Id, SubjectName, CourseOutcomes) values (@Id, @SubjectName, @CourseOutcomes)", con);
                cmd.Parameters.AddWithValue("Id", lblId.Text);
                cmd.Parameters.AddWithValue("SubjectName", lblSubjectName.Text);
                cmd.Parameters.AddWithValue("CourseOutcomes", lblCourseOutcomes.Text);
                

                con.Open();
                int i = cmd.ExecuteNonQuery();
                con.Close();
               refreshdata();

            }

        }
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        
        String strConnString = ConfigurationManager.ConnectionStrings["facultylogConnectionString"].ConnectionString;
        String strQuery = "select CourseOutcomes from CLO where" + " SubjectName = @Subject_Name";
        SqlConnection con = new SqlConnection(strConnString);
        SqlCommand cmd = new SqlCommand();


        cmd.Parameters.AddWithValue("@Subject_Name", DropDownList1.SelectedItem.Value);
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = strQuery;
        cmd.Connection = con;
        try
        {
            con.Open();
            SqlDataReader sdr = cmd.ExecuteReader();
            while (sdr.Read())
            {

                refreshdata();

            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
            con.Close();
            con.Dispose();
        }

    <asp:gridview id="GridView1" runat="server" autogeneratecolumns="False" 
="" backcolor="White" bordercolor="#DEDFDE" borderstyle="None" borderwidth="1px" cellpadding="4" forecolor="Black" gridlines="Vertical" style="margin-top: 142px">  
            <alternatingrowstyle backcolor="White">  
            <columns>  
                <asp:templatefield headertext="ID">  
                    <edititemtemplate>  
                        <asp:textbox id="TextBox1" runat="server" text="<%# Bind("Id") %>">  
                      
                    <itemtemplate>  
                    <asp:label id="Label1" runat="server" text="<%# Bind("Id") %>">  

                      

                  

                <asp:templatefield headertext="Subject Name">  
                    <edititemtemplate>  
                        <asp:textbox id="TextBox2" runat="server" text="<%# Bind("SubjectName") %>">  
                      
                    <itemtemplate>  
                        <asp:label id="Label2" runat="server" text="<%# Bind("SubjectName") %>">  
                      
                  

                <asp:templatefield headertext="Course Outcomes">  
                    <edititemtemplate>  
                        <asp:textbox id="TextBox3" runat="server" text="<%# Bind("CourseOutcomes") %>">  
                      
                    <itemtemplate>  
                        <asp:label id="Label3" runat="server" text="<%# Bind("CourseOutcomes") %>">  
                      
                  
                
                <asp:templatefield headertext="Select Applicable">  
                    <edititemtemplate>  
                        <asp:checkbox id="CheckBox1" runat="server">  
                      
                    <itemtemplate>  
                        <asp:checkbox id="CheckBox1" runat="server">  
                      
                  
              
            <footerstyle backcolor="#CCCC99">  
            <headerstyle backcolor="#6B696B" font-bold="True" forecolor="White">  
            <pagerstyle backcolor="#F7F7DE" forecolor="Black" horizontalalign="Right">  
            <rowstyle backcolor="#F7F7DE">  
            <selectedrowstyle backcolor="#CE5D5A" font-bold="True" forecolor="White">  
            <sortedascendingcellstyle backcolor="#FBFBF2">  
            <sortedascendingheaderstyle backcolor="#848384">  
            <sorteddescendingcellstyle backcolor="#EAEAD3">  
            <sorteddescendingheaderstyle backcolor="#575357">  
          
      
        
        <asp:dropdownlist id="DropDownList1" runat="server" onselectedindexchanged="DropDownList1_SelectedIndexChanged">
        
        
        
      
          
     
         <asp:button id="Button1" runat="server" onclick="Button1_Click" 
="" text="Save to Database">