Dennet doesn't know that he doesn't belief in consciousness. But he doesn't believe in qualia. I interpret that as not believing in consciousness. And, the way he tries to explain consciousness indicates that he thinks that if you explain a system's input-output behavior, you've explained everything about the system.

You seem very confused about Dennett's ideas. He believes in subjective experience; he just thinks that philosophers have used the term "qualia" in misleading and inaccurate ways, and it's better to just talk about subjective experience. He also thinks that it is important to explain people's perceptions of consciousness: he writes about the idea of "heterophenomenology", which is to treat people's perceptions and experience as data that needs to be explained, but is not necessarily completely accurate or reliable.