Charles Ellicott Commentary 2 Chronicles 29:3

"He in the first year of his reign, in the first month, opened the doors of the house of Jehovah, and repaired them." — 2 Chronicles 29:3 (ASV)

THE KING CHARGES THE LEVITES, AND THEY CLEANSE THE HOUSE OF GOD
(2 Chronicles 29:3–19).

In the first month — i.e., in the month Nisan, the first month of the sacred year; not in the first month of his reign. (Compare to 2 Chronicles 29:17 and 2 Chronicles 30:23.)

Opened the doors. —Which his father had closed (2 Chronicles 28:24).

And repaired them. —By overlaying them with metal—bronze or gold-leaf (2 Kings 18:16).