If you are unsure about completing this repair, please stop immediately and seek out a clock professional. If your clock is new and still under warranty, it is best if you find a clock repairman in your area. If this is the only problem, he or she should be able to solve it for you in short order.
Below, you'll see a picture of a bird who has lost contact with the door. Normally, the bird should have a wire going from its "feet" to a staple-shaped wire in the door. This picture is missing that wire:
As you can see, I've drawn (in white) where the wire belongs. I've circled (in red) where the wire loops around the staple-shaped wire lodged in the door. With the wires properly in place, the bird is able to push the door open.
Here's a view from above:
Here (pictured below) is a view from behind the cuckoo bird where you can see the connecting wire that has become unattached from the door. I've circled this push wire in red: