וַיָּ֥שֶׂם אֶת־הַמִּצְנֶ֖פֶת עַל־רֹאשׁ֑וֹ וַיָּ֨שֶׂם עַֽל־הַמִּצְנֶ֜פֶת אֶל־מ֣וּל פָּנָ֗יו אֵ֣ת צִ֤יץ הַזָּהָב֙ נֵ֣זֶר הַקֹּ֔דֶשׁ כַּאֲשֶׁ֛ר צִוָּ֥ה יְהוָ֖ה אֶת־מֹשֶֽׁה׃
And he set the mitre upon his head; and upon the mitre, in front, did he set the golden plate, the holy crown; as the LORD commanded Moses.
Rashi on Leviticus
וישם על המצנפת UPON THE MITRE … DID HE PUT [THE GOLDEN PLATE] — Threads of blue purple that were: fastened on the Plate he put over the mitre, consequently the Plate hung from the mitre mid would be “against his face” (upon his forehead) as stated here (cf. Rashi on Exodus 28:37).
Siftei Chakhamim
On the turban. See above in Parshas Tetzaveh (Shemos 28:37).