Refer the below sample code for your reference and implement it as per your logic.
HTML
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:TextBox ID="datepicker" runat="server" CssClass="classTarget"></asp:TextBox>
<asp:DropDownList AutoPostBack="true" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged"
ID="DropDownList1" runat="server">
<asp:ListItem>Mahendra</asp:ListItem>
<asp:ListItem>Mahendra</asp:ListItem>
<asp:ListItem>Mahendra</asp:ListItem>
<asp:ListItem>Mahendra</asp:ListItem>
</asp:DropDownList>
</ContentTemplate>
<Triggers>
<asp:PostBackTrigger ControlID="DropDownList1" />
</Triggers>
</asp:UpdatePanel>
</div>
<script type="text/javascript">
$(function () {
SetDatePicker();
});
//On UpdatePanel Refresh.
var prm = Sys.WebForms.PageRequestManager.getInstance();
if (prm != null) {
prm.add_endRequest(function (sender, e) {
if (sender._postBackSettings.panelsToUpdate != null) {
SetDatePicker();
}
});
};
function SetDatePicker() {
$('#datepicker').datepicker({ minDate: 0 });
}
</script>
</form>
</body>
Also refer the below link for your understanding.