How do you get the quest from marla stinger to get in sunken city?

To get the quest from Marla Stinger for accessing the Sunken City, you must first reach Level 30 and complete the main storyline that leads you to her. Once you've done that, visit Marla in the Oasis area of the game. She will provide you with the quest that involves gathering specific items or completing certain tasks to unlock the entrance to the Sunken City. Follow her instructions, and you'll be on your way to explore the area.