Refunds can be applied for via the DB Navigator app or the official railway website Bahn.de. Consumer advocates advise caution when applying for refunds online.
Third-party sites are “often opaque” and that people “don’t recognize, or recognize too late, that this is a paid service” If the refund is a larger amount, you only get a part of it because there is a commission or processing fee. If the compensation is less than four euros, it will not be paid out at all.