Rashi: I do not know. The Torah said to offer two lambs [for Musaf] on Shabbos (Bamidbar 28:9)! "Uv'Yom ha'Shabbos" can mean Shabbos Bereishis, and it can mean Yom Tov ¹ . I say that it is Yom Tov, which requires seven lambs and two rams. The verse teaches that they are not Me'akev each other ? if one does not find seven, he offers six. If one does not find two rams, he offers one. This is like Chachamim expounded about Rosh Chodesh.

Radak: This is not the Korban of Shabbos, and not of Yom Tov. Rather, it is a new Korban that will be offered in the future.

Malbim: So they will offer every Shabbos during the 190 days of Chinuch, in addition to the [Torah] Korbanos of the day.