He is to bring to the priest an unblemished ram of proper value from the flock as a guilt offering. Then the priest will make atonement on his behalf for the wrong he has committed in ignorance, and he will be forgiven.
Jewish Publication Society of America Version (JPS1917) - Leviticus 5:18 >And he shall bring a ram without blemish out of the flock, according to thy valuation, for a guilt-offering, unto the priest; and the priest shall make atonement for him concerning the error which he committed, though he knew it not, and he shall be forgiven.