The first word can be "chantez" (imperative) or "chanter" (infinitive), it could also be two words "chante et"..., "tes" is a possessive determiner that must be followed by a noun, it doesn't fit. "apprend" is pronounced "apprahn" but "apprendre" is pronounced "apprahnd" in the most casual case.
I recorded this first part and slowed down the tempo but it doesn't help much. When I first heard it, I heard "chantez... la France, dansez, dansez, dansez dans les prés" but I thought it was recorded much later WW II to tell the French to sing and go dance in the meadows. It can't be "allégré", there isn't such a word, "allez gré" doesn't mean anything. I hear it as some "vré" but there's no "vré", only "vrai" (true) and it doesn't make more sense. Well, as we say, "c'est clair comme du jus de boudin" (literal translation: it's as clear as black pudding juice)