Changing the date and/or departure time or cancelling train tickets is only possible if the terms and conditions allow it.
Flexible fares have less or no exchange or cancellation fees than non-flexible fares. Generally speaking, non-flex fares cannot be cancelled or exchanged.
The specific terms and conditions for the booking you have made are explained for each ticket in My NSI.
When you bought your ticket on NSInternational.com or by telephone from NS International Customer Service, go to the Change or cancel your trip page.
When you bought your ticket at a Service office with a NS International desk or from a travel agent? Contact or visit your original point of sale. They will help you with your request.