If you are registered with IRCTC then log in
then
2- Look for tab "Tourism"
3- It has Accommodations Tab which opens two links Hotels and Retiring rooms
4- clicking Retiring Rooms will...
more... get you a page you will have to again Log in
5- after log in you get the page that enables you to fill up form starting with PNR and then follow the easy steps of booking at origin or destination
Try once and you get to know how it is done