To start the Murder on Eridanos DLC, you’ll simply need to wait for ADA to mention that she’s about ready to watch the Halcyon Helen Aetherwave. As a side note, it took a little more effort to get the DLC set up on the PS5. The Murder on Eridanos was registered as being owned but we had to find it in the Playstation Store and add it to our library. After doing that, we were able to access the DLC in the game.