10 Once a year Aaron shall make atonement on its horns. This annual atonement must be made with the blood of the atoning sin offeringa for the generations to come. It is most holy to the LORD.”

Read Exodus 30:10 Using Other Translations

And Aaron shall make an atonement upon the horns of it once in a year with the blood of the sin offering of atonements: once in the year shall he make atonement upon it throughout your generations: it is most holy unto the LORD.
Aaron shall make atonement on its horns once a year. With the blood of the sin offering of atonement he shall make atonement for it once in the year throughout your generations. It is most holy to the LORD."
“Once a year Aaron must purify the altar by smearing its horns with blood from the offering made to purify the people from their sin. This will be a regular, annual event from generation to generation, for this is the LORD ’s most holy altar.”