Getting second configuration descriptor of usb device

Official Hardware Mega Due
1

My usb device has total two configuration descriptor.
After checking vid and pid of usb device i am parsing configuration descriptor using ConfigDescParser method but by default it is getting first configuration descriptor.
How to get second configuration descriptor and parse it.
I am using Arduin 1.5.4 USBHost Library

if(((USB_DEVICE_DESCRIPTOR*)buf)->idVendor == VID &&

(((USB_DEVICE_DESCRIPTOR*)buf)->idProduct == PID )){

for (uint32_t i = 0; i < num_of_conf; ++i)
{
ConfigDescParser<0, 0, 0, 0> confDescrParser(this);
delay(1);
rcode = pUsb->getConfDescr(bAddress, 0, i, &confDescrParser);
}
}