Rear spoiler C5 estate, no visible screws inside tailgate.

There is a plastic trim piece that needs to be removed to get to the screws for the spoiler. The top brake light should be secured in the spoiler by screws from the outside.

Your vehicle isn't available in the U.S. So our reference doesn't list it and I'm unable to find any images I can use that help me visualize what you have. From experience with other cars, there should be two screws securing the LED lens to the spoiler.