As other experts suggested,cookies can not be deleted directly on user's computer,but you can do something tricky e.g.
setting the cookie's expiration date to a past date.
if (Request.Cookies["YourCookies"] != null)
{
Response.Cookies["YourCookiesCookies"].Expires = DateTime.Now.AddDays(-1);
Response.Redirect("Redirect to xyz.aspx");
}
For more information refer to below links
How to: Delete a Cookie[MSDN][
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Basics of Cookies in ASP.NET[
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