You'll need to finish up Extreme Simplicity first, cause trying earlier just won't work. Once that's done make your way to SIRCAA's main building and when security stops you, just play nice and answer all their questions. Inside, Dalin himself will actually come meet you and give you his Green Key Card which is what you're looking for. The elevator to his suite is pretty easy to spot, just look for it at the left end of the main hallway on the ground floor.

Something interesting - his suite has some good stuff hidden around, especially a wall safe that needs a journal note to crack open. There's this thing called the Battery artifact in there that's really worth grabbing. Also, memorizing the layout of this place isn't a bad idea, cause you'll definitely be back here later when things get way more intense and knowing your way around definitely helps when you're under pressure. If you're planning to rest in the suite which you'll need to do for some missions later, maybe grab everything useful first, cause some story stuff triggers after sleeping.