FYI, this is the script

$scopes = Get-DhcpServerV4Scope

foreach ($scope in $scopes)

{

 $reservs = get-dhcpserverv4reservation -ScopeID $scope

  foreach ($reserv in $reservs)

   {

     Set-DHCPServerv4DNSSetting -IPAddress $reserv.IPAddress -DynamicUpdates Never

   }

}