It is not the cuckoo that goes wrong, but the hour-hand is in the wrong position.
To set the hour hand, you can pull the hand at the attachment point on the handshaft, pulling towards the minute hand until it is loose, reposition the hand to the proper hour, and push the hand towards the dial until it is tight.
Important: If your clock uses wooden hands you may need a little glue (cyanoacrylat “super glue”) to attach the hand again, but please be very careful with the glue.