In order to access the Exodus Siege Adventure, you must have completed the Missions Looped and Six. It is recommended to attempt this adventure at Level 90.
Head towards the marker and find the Cloaked Scout to the left of the area.
After interacting with the Scout, head to the next waypoint.
At the point, you will need to kill the Fallen wandering around the area until your counter is at 100%. There are several bombs in the field that you can shoot down to boost your percentage up.
Follow the waypoint into the cave and use the teleporter. Keep following the waypoint until you see an Assault Servitor.
Take out the Servitor and collect the Arc Charge that it drops. Take out the Fallen wandering around the area before collecting the Arc Charge, then place the Arc Charge in the hole that is marked after defeating the Fallen.
At the next area you will have to repeat the previous proceed two times. After overriding the Generators, a Fallen Commander will appear.
The Fallen Commander, Elyskul, is very easy to take down if he is alone, so eliminate the enemies accompanying him before dealing with him.
You will be rewarded with a Rare Blue Loot for defeating the boss and finishing the Exodus Siege adventure.