Unlike Moses who taught the people a song, the Lamb did not teach a song. Instead, the Lamb is the content of songs sung earlier in Revelation (Revelation 5:9–10, Revelation 5:12–13). Themes of those songs also come back in the song the redeemed sing in Revelation 15:3–4.
3 And they sing the song of Moses, the servant of God, and the song of the Lamb, saying, “Great and amazing are your deeds, O Lord God the Almighty! Just and true are your ways, O King of the nations!