how to Redirect the selected value DropDown List

You need to handle the SelectedIndexChanged event and then do the Response.Redirect in the handler.

something like below may helps you.

<asp:DropDownList ID="ddlValues" OnSelectedIndexChanged="ddlValues_OnSelectedIndexChanged"
        runat="server">
        <asp:ListItem Text="Apple" Value="1"></asp:ListItem>
        <asp:ListItem Text="Microsoft" Value="2"></asp:ListItem>
    </asp:DropDownList>

protected void ddlValues_OnSelectedIndexChanged(object sender, EventArgs e)
    {
        Response.Redirect("YouURL.aspx?Value=" + ddlValues.SelectedValue);
    }

If DropDownList1.SelectedValue = "1" Then
Response.Redirect(("Form1.aspx?Value=" + DropDownList1.SelectedValue))
ElseIf DropDownList1.SelectedValue = "2" Then
Response.Redirect(("Form2.aspx?Value=" + DropDownList1.SelectedValue))
ElseIf DropDownList1.SelectedValue = "3" Then
Response.Redirect(("Form1.aspx?Value=" + DropDownList1.SelectedValue))
End If