Yes, it is possible to retrieve reservations that were canceled by mistake.
This is how you can do that:
Go to the Reservation panel
Make sure you've chosen the right date for the reservation
You need to filter canceled reservations. There are two options for doing that:
Using the "eye filter" on the top right part of the screen
Using the filter on the top left part of the screen (select "Show Closed/Canceled")
You will be able to see all canceled and closed reservations.
They will show in a very light grey colour and therefore, it will be easier to differentiate them from active reservations.
Click on the reservation that you want to retrieve.
The reservation card will appear on the right side of the screen.
Select "Reopen" on the reservation card.
You have successfully retrieved this reservation!