TT #208 · Parshas Tazria · Aliyah 5 · Passuk 33
English: he shall shave himself, but he shall not shave the netek; and the priest shall isolate the netek for a second seven-day period.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:33
Torah Temimah cites Sifra (Toras Kohanim) for the prohibition against removing signs of impurity from a netek.
Sifra — Vayikra 13, Midrash Sefer
English: How do we know that plucking a sign of impurity from a lesion violates a prohibition? The Sifra derives it from the command, “He shall not shave the netek.”
Textual derivation
The command not to shave the netek also prohibits deliberately removing the signs that determine its status.