Contact KLM or the Airline: As soon as you realize that you've missed your flight, contact KLM Missed Flight or the airline immediately. You can usually find the airline's customer service phone number on their website or your booking confirmation. Explain your situation and provide your booking reference, ticket number, and any other relevant details.

Rebooking Options: Ask the airline about your rebooking options. Depending on the fare type, ticket conditions, and availability, you may be able to reschedule your flight for a later time on the same day or for a different day. Be prepared for the possibility of paying a change fee and any fare difference if your original ticket was non-refundable.
Standby: If there are available flights later in the day or on the next day, KLM may put you on standby for those flights. This option depends on seat availability and the airline's policies.