Quick answer: enter the Sewers as Priest, find the Cult Ritual encounter, and complete its assistance route.
Checklist
- Start as Priest.
- Take the route that reaches the Sewers.
- Prioritize Cult Ritual when it appears.
- Choose the dialogue path that aids and completes the ritual.
Community guides agree on the class and encounter. Because event dialogue is version-sensitive, the wiki avoids presenting an old click-by-click sequence as permanent.