Thanks sir its worked :)
I would like to tell that how its work so that other people can get help by it
create a new page and then apply the server behavior "MySQLi Logout User" with the trigger "before page loads". Then any link to that page would work as a logout link.in your new page your code will be like this:
if ("" === "") {
$LogOut = new WA_MySQLi_Auth();
$LogOut->Action = "logout";
$LogOut->Name = "loginForm";
$LogOut->execute();
}
add $LogOut->Redirect("your_login_page.php); before $LogOut->execute();
Thanks