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You're looking for the Experience PlayStation app (Google Play link [link] )
However, they haven't put anything on there for East 2019 yet. They didn't use the app for South 2019 so who knows.
Playstation! To test out any PS4 games or to attend a private demo screening you'll have to download the Experience Playstation app developed by PlayStation Mobile Inc.
This app kind of works like reserving movie tickets in that there's a ton of time slots for different games or screenings and I want to say at 9AM everyone is able to try to reserve a slot. Now imagine around 10,000 people trying to use this app all at once, it will lag so bad. On the second day of E3 my friend and I went to a coffee shop with free wifi to use the app and we lucked out and reserved 2 spots for a screening of Spiderman and Days Gone. I think 2 reservations was the max for game screenings, not sure about game demos. You can't even get in line to test out a game unless you show the Playstation employee your app with the reservation on it.
I think they are already filled up for today, but you can try again tomorrow. Registrations typically open at 10am.
It is called Experience PlayStation in the Google Play Store as well.