Use
You can replace one booking with another if an attendee booked for a business event cannot take part in it for whatever reason.
Features
Replacing individual attendees

However, a dialog box appears querying whether you want to enter different settlement data for the new attendee.
Replacing N.N. bookings

An N.N. booking with 5 attendees for an organizational unit can be replaced with a booking for 2 other members of an organizational unit. The remaining 3 original bookings are still valid.
Result
The original booking is deleted.
The new attendance is booked.
See also:
Replacing Attendance