You can make changes to your ticket using the offline process. You need to reach out to the reservation of KLM; you can ring 1-800-618-0104 and tell them that you want to change your ticket; you have to tell them your pnr and your last name and tell them what changes you want in your ticket.
Ticket holders must know that after the free window of change is over, you have to pay a cost to make changes to your ticket and that amount is $150 to $200, varying per your travel class and itinerary of your travel.
KLM travelers can make changes using a policy of change and following one of the explained processes or making changes to their ticket to make these changes without fee of change; however, there is a cancelation price for making changes after a free period of the window per policy.