pf2e.fyi
From Pathfinder Lost Omens Hellfire Dispatches, which isn't enabled.

Order Cross-Training

FEAT 12
ARCHETYPE
Archetype Hellknight
Prerequisites Hellknight Dedication

You gain the lesser order benefit of a Hellknight order other than the one to which you belong. This represents your time spent training with members of that order to learn their techniques and teachings. If you aren't in good standing with a given order, you can't receive their training.

Special You can select this feat multiple times, gaining the lesser order benefit from a different order each time by training with members of that order.
Pathfinder Lost Omens Hellfire DispatchesORC