If you want to un-cancel a booking that you have already cancelled, you should go to the booking view page and Edit the booking.
Make sure the price of the booking is what you want it to be, change the Booking Status to Booked and Save.
If the booking was Paid, or its deposit was authorised, when you cancel the booking, the payment amount will be set as the Cancellation Penalty under Security Deposit Charges Title.
After un-cancelling the booking, the payment amounts will be reallocated to the booking and the Cancellation Penalty gets Disapproved.
If the booking was Unpaid, the un-cancelled booking will be Unpaid as well.