Hi there,
You can simply visit there website, railrider.in or call at 0-81048-81048 (7AM - 10PM).
If you are going for website, then follow the below steps
Enter PNR or Train Number.
Choose your favorite...
more... food.
Pay online or cash on delivery.
Enjoy your food on your selected station.
You need to order 1 hour before, your train come at station you choose.