As far as I'm aware, that scene is not repeatable right now. You would need to create a separate save right before the scene to revisit it.
I very much hope that this scene will be repeatable in the future. Otherwise it'd just be a waste of scripting and artwork.
You need to have had the scenes where Julie almost walks in on you and Linda in the bathroom, as well when Julie walks in on you and Linda in your bedroom. You also need to have reached the "end" of Linda and Julie's solo storylines. I'm not sure if you need to have had the scene with Julie by the pool during the day.
Keep talking to Julie, she will give you instructions to watch her in the pool at night.