An extension works exactly the same as a rental request. In the booking overview, your renter can send a rental request. This request has a new end date and time for the current booking. If you agree and the car is available, you accept the request. The renter can then pay the extension, finalising the new rental end date and time.
If you do not wish to accept the booking, please decline the extension request and inform the renter. The rental period will end on the original date and time.
Note that if you do not accept the extension request 1 hour before the original end time, the rental request will be automatically denied.