Desvendar means to 'unravel', 'uncover', or 'solve'. It's a less common verb than simply 'to understand', carrying a sense of mystery and effort in discovery.
In the song, Marília Mendonça sings, "'To tentando desvendar o meu relógio / Pra entender o tempo" (I'm trying to unravel my clock / To understand time). She uses desvendar to express her deep struggle to comprehend the passage of time and the missed opportunities, making it a poignant and engaging word choice.
A phone call on a birthday that should have gone differently. The singer admits "Se eu não tivesse errado, demorado" (If I hadn't made a mistake, delayed) she would still be the one standing beside the person she's calling, but the mistake happened, and now all she has left is a call: "Liguei pra te dar parabéns" (I called to wish you happy birthday). The chorus circles back to that same short list of gifts a phone call can carry — "Ninguém consegue ocupar o seu lugar" (Nobody can take your place) — because there's nothing else left to give.
By the second verse, the address shifts and Maiara and Marília sing to each other by name, turning the birthday song into a duet between friends rather than a plea to an ex. It's a song about outliving a regret: you can't undo what went wrong, but you can still show up on the day that matters, even if all you can offer is a call.