The Zoroastrian term for one’s own conscience or religion is Daena.
Daena is an Avestan concept associated with insight, spiritual awareness, conscience, faith, and religious law. The word continued into Middle Persian as den and into modern Persian as din, meaning religion. It can therefore describe both a person’s inner moral vision and the religious path shaped by that vision.
In Zoroastrian teachings, a person’s choices strengthen or weaken the Daena. Later Avestan tradition gives it a striking afterlife image: on the fourth day after death, the soul encounters its own Daena in human form. For a righteous person she appears beautiful; for a wicked person she appears frightening, reflecting the life that person led.
Daena is sometimes confused with Asha, the principle of truth and cosmic order, or with a Fravashi, a protective spiritual essence. Those are related Zoroastrian ideas, but they are not the canonical answer to this question.