The official website does not explain what to do in that scenario but the DB is very specific about it: You have to travel with the exact (credit or ID) card registered as a token when you booked the ticket, no exceptions. If the card expired, you are expected to present the old, expired card instead of the new one (or possibly both if you are travelling with a Bahncard). And it does not seem possible to change the token, even in person and with a very good reason, let alone online or from abroad.
Various forum posts (from people who had their credit card or ID card stolen or from DB support staff answering their questions) all confirm that you really are supposed to buy a new ticket, even if you can present another ID and some document from the police confirming the previous one was stolen. Rail guards do have the option to let it slip but apparently the recommended procedure is to charge you for the - current and therefore possibly higher - price of a ticket with a small surcharge (Bordpreis) and invite you to ask the customer service for a (partial) refund as a commercial gesture (Kulanz).
At this point, it therefore seems that you have the choice between two (bad) options:
- Cancel your ticket and buy another one. It will cost you some but at least you know exactly how much and you have some peace of mind during the trip.
- Try your luck, with the downside being that you might be forced to buy an even more expensive ticket in the train. Not necessarily the end of the world but rather frustrating. Seeking out a member of the crew as soon as possible rather than waiting for them to come to your seat can also be a good idea.
No matter what you do, you can also try your luck with the customer service afterward but that sounds like a lot of hassle for a foreign resident. In any case, they are unlikely to issue a full refund and typically give out vouchers (Gutschein) for future train travel rather than cold hard cash, which is probably not very useful for you.