Eldritch Adept

Spellcasting or Pact Magic feature

Studying occult lore, you have unlocked eldritch power within yourself: you learn one Eldritch Invocation option of your choice from the warlock class. If the invocation has a prerequisite, you can choose that invocation only if you’re a warlock and only if you meet the prerequisite.   Whenever you gain a level, you can replace the invocation with another one from the warlock class.