The Linking Ritual is the next side mission from Aphra. The guide to GreedFall contains a walkthrough of this quest.
Where to start the quest?: Talk to Aphra after completing earlier tasks for her.
Wait 24 hours for the ritual to begin. Then go to Cergganaw to begin the ritual. Talk to the members of Dunncas' clan and then stand in the specified location to begin the ritual.
After a cut-scene, a large group of soldiers of the Bridge Alliance will appear. Protect the natives.
After a few dialogs, the mission will end. You get 1600 XP and +3 rep with Aphra.