TT #286 · Parshas Tazria · Aliyah 7 · Passuk 54
English: The priest shall command that they wash the article in which the lesion is found, and he shall isolate it another seven days.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:54
Torah Temimah cites Sifra (Toras Kohanim) for the division between the priest’s command and the act of washing.
Sifra — Vayikra 13, Midrash Sefer
English: The priest gives the command, while the washing may be done by anyone.
Textual derivation
The priest issues the command to wash the garment, but the washing itself may be performed by any person.