In the case of a train booking including multiple passengers, you can modify or cancel the train ticket of one of the concerned passengers directly from the platform.
To do this, you have two options.
You must:
either modify or cancel the entire train ticket of the concerned passenger (both outbound and return), then proceed with a new booking for this passenger
or modify or cancel one of the train ticket trips (outbound or return) for ALL passengers involved in the group booking, then proceed with a new booking for all passengers
🧐 Please note: it is not possible to modify or cancel a single trip segment (outbound or return) for just one of the passengers involved in the group booking.