Whoever deals with the paperwork should be notifying the appropriate
TOC▸ .
Will find the entry in "The Manual" for you.
Edited to add:
Replacement for damaged or ^Encoding Failure^
If a valid weekly or period Season Ticket/Travelcard is damaged, or can^t be read easily, or no longer opens automatic gates, it can be replaced free of charge (using appropriate ^Replacement Ticket^ stock) at any National Rail station ticket office on the route or in the zone/s that it is valid for. If the ticket is unreadable, refer the customer to the issuing office of the ticket, who may issue a replacement if the details of the ticket sale can be verified or the customer^s records can be checked.
All tickets issued by Transport for London stations (formerly London Underground, London Buses, Docklands Light Railway and London Tramlink) may only be replaced at their respective stations and offices.
In case of other than weekly Season Tickets/Travelcards, the record at the original issuing station/telesales retailer must be updated to record that a replacement has been issued. The office issuing the replacement should complete the form ^Advice of Replacement of Damaged/Encoding Failed Season Tickets^ RSP 25805/31 (or the equivalent Train Company/third party retailer authorised document):
Send top copy to the station that originally issued the Season Ticket;
Retain the second and third copies.
A Season Ticket/Travelcard/Annual Gold Card may be replaced whenever necessary, without limit on the number of occasions.
Specially printed tickets bear the overprint ^Replacement^ on the lower part.