Here "he" refers to the one making the offering. It can be stated in second person. Alternate translation: "Then you must kill the bull" (See: [[rc://en/ta/man/translate/figs-123person]])
It is implied that the priests would catch the blood in a bowl as it drained out of the animal. Then they would bring the bowl with the blood in it and present it to Yahweh at the altar. (See: [[rc://en/ta/man/translate/figs-explicit]])