Forum:Returning to Hephaestus

I finished Hephaestus without collecting all of the audio diaries in the Hephaestus section (not Rapture Central Control because I know that you can only get those once). I just finished getting through Apollo Square and can go to Point Prometheus. How can I go back to Hephaestus because I don't seem to be able to change the destination for the bathysphere from Point Prometheus.