Hi nauna,

Check this example. Now please take its reference and correct your code.

HTML

<asp:DropDownList ID="ddlTimeZones" runat="server" AppendDataBoundItems="true">
    <asp:ListItem Text="Select" Value="0" />
</asp:DropDownList>

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        List<ListItem> items = new List<ListItem>();
        foreach (TimeZoneInfo tzi in TimeZoneInfo.GetSystemTimeZones())
        {
            items.Add(new ListItem { Text = tzi.DisplayName, Value = tzi.Id });
        }
        ddlTimeZones.DataSource = items;
        ddlTimeZones.DataTextField = "Text";
        ddlTimeZones.DataValueField = "value";
        ddlTimeZones.DataBind();
        if (ddlTimeZones.Items.FindByValue(TimeZone.CurrentTimeZone.StandardName) != null)
        {
            ddlTimeZones.Items.FindByValue(TimeZone.CurrentTimeZone.StandardName).Selected = true;
        }
    }
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim items As List(Of ListItem) = New List(Of ListItem)
        For Each tzi As TimeZoneInfo In TimeZoneInfo.GetSystemTimeZones()
            items.Add(New ListItem With {
                .Text = tzi.DisplayName,
                .Value = tzi.Id
            })
        Next

        ddlTimeZones.DataSource = items
        ddlTimeZones.DataTextField = "Text"
        ddlTimeZones.DataValueField = "value"
        ddlTimeZones.DataBind()
        If ddlTimeZones.Items.FindByValue(TimeZone.CurrentTimeZone.StandardName) IsNot Nothing Then
            ddlTimeZones.Items.FindByValue(TimeZone.CurrentTimeZone.StandardName).Selected = True
        End If
    End If
End Sub