The textbox should load the value from the database

<asp:ScriptManager ID="ScriptManager1" runat="server" />


    <asp:UpdatePanel ID="UpdatePanel25" runat="server" UpdateMode="Conditional">


<ContentTemplate >
  <asp:TextBox ID="TextBox23" runat="server"
            style="z-index: 1; left: 747px; top: 180px; position: absolute"
            ontextchanged="TextBox23_TextChanged" AutoPostBack="True"></asp:TextBox>
        </ContentTemplate>
        <Triggers>
        <asp:AsyncPostBackTrigger ControlID="TextBox23" EventName="TextChanged" />
        </Triggers>



    </asp:UpdatePanel>

protected void TextBox23_TextChanged(object sender, EventArgs e)   // loginID
    {
        v_liginid = TextBox23.Text; // line 1
        
    con.Open();
    SqlCommand cmd = new SqlCommand("select * from member where liginid = @v_liginid", con); 
    SqlParameter param = new SqlParameter();
    param.ParameterName = "@v_liginid"; 
    param.Value = TextBox23.Text; 
    cmd.Parameters.Add(param); 
    SqlDataReader reader = cmd.ExecuteReader(); 
        if (reader.HasRows) 
    {
        Label55.Visible=true;
    } 
    }