John Gill Commentary 2 Chronicles 29:22

"So they killed the bullocks, and the priests received the blood, and sprinkled it on the altar: and they killed the rams, and sprinkled the blood upon the altar: they killed also the lambs, and sprinkled the blood upon the altar." — 2 Chronicles 29:22 (ASV)

So they killed the bullocks
The seven bullocks, that is, the priests killed them: and the priests received the blood ;
into basins provided for that purpose: and sprinkled it on the altar ;
according to the law of Moses, (Leviticus 1:5) and so they did with the rams and lambs.