The plus-que-parfait is formed by conjugating the auxiliary “avoir” or “être” (depending on the verb) into the imperfect tense then adding the past participle of the verb.
Here are the most common verbs used with the auxiliary “être”: aller, apparaître, arriver, décéder, demeurer, devenir/redevenir, entrer/rentrer, intervenir, naitre, partir/repartir, rester, tomber, venir/revenir.