After seeing many simulations of the command/service module doing a 180 and docking with the LEM, it occured to me that something didn't look right. At the nose of the command module there appears to be a triangular steel structure, which I am assuming it's purpose is to complete a hard dock. But with this structure in place, how was it possible for astronauts to travel back and forth between the LEM and command module?
That structure was just a probe to establish soft dock. Similar to an aerial refueling probe, the probe would latch on to a conical “drogue” element on the lunar module (soft dock). Then, it would retract to precisely align the docking rings to seal together and lock (hard dock).
After hard dock, crew would manually remove the probe and drogue and stow them internally on the spacecraft. This left a circular passage between the two spacecraft.
See this question and answer for more details: Help understanding this Apollo 11 docking probe image, what are we looking at, and from where?