Numbers 19:8

19:8 The one who burns it ¹  must wash his clothes in water and bathe himself in water. He will be ceremonially unclean until evening.

Numbers 19:19

19:19 And the clean person must sprinkle the unclean on the third day and on the seventh day; and on the seventh day he must purify him, ²  and then he must wash his clothes, and bathe in water, and he will be clean in the evening.

¹ sn Here the text makes clear that he had at least one assistant.

² tn The construction uses a simple Piel of חָטָא (khata’, “to purify”) with a pronominal suffix – “he shall purify him.” Some commentators take this to mean that after he sprinkles the unclean then he must purify himself. But that would not be the most natural way to read this form.