This page explains how to complete the level 90 post-Endwalker quest "Return from the Void".
This quest is available if you have completed the quest The Wind Rises.
Starting the Quest
Talk to Varshahn in Zero's Domain (accessible from the Fell Court of Troia, which is accessible from Thavnair) to begin the quest. There will be a cutscene.
Speak with the Deserter Voidsent
Go north to go outside, then go northwest to where the orange arrow is pointing in the minimap.
Speak with Varshahn
Go southeast and enter Zero's room, and talk to Varshahn. You will not be able to freely return to the Thirteenth, so if you want to explore the area before you depart, say No. Otherwise, if you are ready, say Yes, and there will be a cutscene.
Speak with the Meghaduta Attendant
Go to the quest icon and talk to the Meghaduta Attendant, and say Yes to complete the quest. There will be a cutscene.
Next Main Scenario Quest
After you complete the quest, talk to Y'shtola to accept the next quest: A World with Light and Life.