Source: As worded by Indian Railways, Government of India

In such cases, you must obtain a Ticket Deposit Receipt (TDR) from the nearest major station within 30 days from the date of scheduled travel. You must then submit an application in the prescribed from( Printed on the back of TDR) to the Chief Commercial Manager (Refunds) of the Zonal Railway to which the Ticket Deposit Receipt-issuing station belongs.

This application must be submitted within 90 days from the date of your journey. The refund officer will examine the case on merit and, if decided, refund will be sent to you by a Station Pay Order (to be encashed at station) or Money Order or Crossed Cheque.