Capítulo literally translates to "chapter", as in a chapter of a book. This word perfectly captures the hopeful theme of the song.
In the chorus, Becky G sings, "Vamos a empezar otro capítulo" (Let's start another chapter). She uses this as a beautiful metaphor for getting a second chance at love, suggesting they can leave the past behind and start a fresh, new page in their story together.
Ever run into an ex and realize... oops, the feelings are still there? That's exactly where Becky G finds herself in this song. She sees an old flame after a long time and admits that while a lot has changed, her desire for him hasn't: "Pero las ganas de tenerte, baby / Esas siguen igual" (But the desire to have you, baby / That's still the same). She even feels like she wasted her time "Buscando en otros lo que tú me das" (Looking in others for what you give me).
Instead of getting stuck on their history, she has a simple, direct proposal. She argues that giving it another shot wasn't in her plans, but since it's happening, why fight it? She asks, "¿Y si nos besamos como antes?" (And what if we kiss like before?). Her solution is to forget the past and just move forward. As she puts it, "Lo que pasó, baby, ya pasó / Vamos a empezar otro capítulo" (What happened, baby, already happened / Let's start another chapter).