This page explains how to complete the level 80 post-Shadowbringers quest "Forget Us Not".
This quest is available if you have completed the quest Reviving the Legacy.
Starting the Quest
Talk to Alisaie in the Rising Stones in Mor Dhona to begin the quest.
Speak with Alisaie at Maelstrom Command
Teleport to Limsa Lominsa and use the Aetheryte to go to the Aftcastle. Go east to the quest icon and talk to Alisaie to proceed. There will be a cutscene.
Speak with Alphinaud
Talk to Alphinaud 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: Like Master, Like Pupil.