The Initiate Sequence mission in Watch Dogs: Legion is the first mission in the 404 Chapter. In this mission, you are required to go to the Walkie Talkie Club after receiving a message from the ctOS Hub.
Once you reach the Walkie Talkie Club, you will have to board an elevator to the upper floor. On reaching there, you will be asked to access the Facial Recognition AI. This is where things get a bit tricky since there is no way to get past this area and reach the objective marker indicated on the screen.
What you actually have to do here is use your Spider-Bot. After reaching the upper floor, go upstairs toward the right. You will find a plant with a white concrete base; just below it will be a vent. Throw your Spider-Bot near the vent and interact with it to open it.
Keep going straight until you reach the end of the vent and fall into another room. You will see many people there; thankfully, none of them will spot you and raise the alarm. Towards the end of the room, there will be another vent in the bottom. Go inside it to reach another room.
Hop onto the desk in front of you and on to the next one from there. Just above the second desk will be another vent that you need to hop into. Proceed through the vent to finally reach the room, which contains the Facial Recognition AI.
Get close to the ctOS terminal inside the room, and you will get an option to interact with it when the Spider-Bot reaches the small switch at the bottom. Interact with it to complete the mission and proceed further.