Replacement and handling the lost key are separate questions
With no working key, begin by checking whether a suitable replacement can be made. If a key remains, mention it: you can ask about a spare and the options for addressing recognition of the missing key.
Explain if you believe someone else may have the key. Sensitive identifying details do not need to be posted publicly. Arrange directly which details are needed to check the vehicle and book the service.
What does changing key recognition mean?
The options for changing which keys the system recognizes depend on the vehicle and proposed action. Ask which functions of the old key will be affected and which will remain unchanged. A general statement about programming is not enough to explain the result.
A blade that fits a lock is a mechanical component. Changes to starting recognition do not prove that the old blade can no longer unlock a door. Raise mechanical locking separately if it needs attention.
Include the remaining keys in the arrangements
List who holds other keys and which ones unlock and start the car. Before a visit, confirm which keys must be available with the vehicle. Mention a key held by another driver even if it is rarely used.
Afterwards, check the agreed keys and functions with the service provider. Ask what was changed in the system and how to check a key that was unavailable during the work.
If the old key is found after the work
Do not treat it as a reliable spare simply because it opens a door. Report that it has been found and ask how to check it against the work performed. A mechanically compatible key may still lack a particular electronic function.
Describe which functions it performs and keep it separate until the enquiry is complete. That avoids depending on an unverified key as your only backup.
Company cars, rentals and other drivers
If you do not own the vehicle, inform whoever manages it and arrange the service with them. They may have another key or instructions for handling the incident. Reporting duties and costs depend on the relevant agreement and organization.
Say who is coordinating and whether a key remains. You can begin by checking the suitable service before deciding what to order.
What to check when handing car keys to someone else