You can find the information about the number of extended bookings and their value for the selected period in Booking Channel Summary report.

In the last part of the report, you will see two charts which show information per booking method:

Total number of extended nights

Total Value of extended nights

The information in the report can be shown for the whole selected period or per days

You can find this option in the top of the report, here:

Check also:

Extend the booking

Booking Methods

How to add another person or a room type to an existing booking