Asp.net gridview's edit button doesn't edit the page I want

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C#

ASP.NET

Gridview

database

Teacher logins and selects which lecture it would like to update student's grades. When it clicks button, Gridview retrieves student infomations and grades. When teacher clicks GridView's edit button, GridView automatically editing the first table which loaded in "pageload". How can I edit the page I want? To visualize :

1- When page loaded normally

2- After selecting lecture and retrieving student informations (The page I want to edit).

3- After clicking GridView's edit button. It edits wrong page. I want to edit the table in second image.

Image 1
Image 2
Image 3

protected void Page_Load(object sender, EventArgs e)
    {
        //Retrieving teacher's lectures from database to dropdownlist.

        //Sidebar kısmında isim ve numara labellarina verilerini atar
        UsernameLabel.Text = Session["UsernameSession"].ToString();
        UsernumberLabel.Text = Session["UsernumberSession"].ToString();

        //Dropdownlist içerisine giriş yapan öğretmenin derslerini çağırma işlemi
        if (!IsPostBack)
        {
            OleDbConnection baglanti = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:/Users/ERKAN/Desktop/Sinav/Sinav/Veritaban.mdb");
            baglanti.Open();

            OleDbDataAdapter adptr2 = new OleDbDataAdapter("Select * FROM Dersler Where DersOgretmeni='" + UsernameLabel.Text + "'", baglanti);

            DataTable tbl = new DataTable();

            adptr2.Fill(tbl);

            DropDownDers.DataSource = tbl;

            DropDownDers.DataValueField = "DersAdi";
            DropDownDers.DataBind();
            baglanti.Close();
            baglanti.Dispose();


            //Dropdownlist içerisine dersleri çağırma işlemi

            //Gridview içerisine dersleri alan öğrencileri çağırma işlemi

        }

    }

    protected void Kaydet_Click(object sender, EventArgs e)
    {
       //Retvieving student informations from database to gridview.

        if (this.IsPostBack)
        {
           
            Veritabansource.SelectCommand = "Select [ID], [Ogrenciler], [OgrenciNotu] From "+DropDownDers.SelectedItem.ToString()+"";
            Veritabansource.DeleteCommand = "DELETE FROM [" + DropDownDers.SelectedItem.ToString() + "] WHERE [ID] = ? AND (([Ogrenciler] = ?) OR ([Ogrenciler] IS NULL AND ? IS NULL)) AND (([OgrenciNotu] = ?) OR ([OgrenciNotu] IS NULL AND ? IS NULL))";
            Veritabansource.UpdateCommand = "UPDATE["+DropDownDers.SelectedItem.ToString()+"] SET[Ogrenciler] = ?, [OgrenciNotu] = ? WHERE[ID] = ? AND(([Ogrenciler] = ?) OR([Ogrenciler] IS NULL AND ? IS NULL)) AND(([OgrenciNotu] = ?) OR([OgrenciNotu] IS NULL AND ? IS NULL))";
            Veritabansource.DataBind();
            GridView1.DataBind();
        }
        //Butona basınca seçilen dersin öğrencilerinin gelmesi işlemi

       //Resim atama işlemini yapmadım
    }

What I have tried:

I tried to change updatecommand of datasource when teacher clicks the "Kaydet" button.