Candela literally means "candle" or "fire". However, in many Latin American contexts, especially in music, it's used colloquially to mean "passion," "intensity," or even "trouble."
In this song, when the lyrics say "Tres viejas con candela," it implies three women with a lot of fire, passion, or intense energy, adding a vibrant and engaging image to the narrative.
The whole song happens on a phone screen. The narrator opens by admitting he is lost and refusing to admit it in the same breath — "Ando un poco perdido / Se me nota, pero no te lo digo" (I'm a little lost / It shows, but I'm not telling you) — and everything after that is him proving it. He is up scrolling her stories, "Vengo checando las historias y me saca de onda" (I keep checking the stories and it throws me off), and sizing up whoever replaced him, "Ese puto no te controla, tampoco te checa" (That idiot doesn't keep tabs on you, doesn't even check on you). They already agreed to be friends — "Ya quedamos como amigos" — and he is drinking about it anyway: "Ando tomando por ti, por ti, por ti" (I'm drinking because of you, you, you).
The chorus is the part he will not say to her face. "Y dejé, dejé, dejé huellas en tu piel" (And I left, left, left marks on your skin) is the one piece of evidence he has that it was real, and "Mami, ponte otra vez / Sabes que lo haces muy bien" (Baby, put it back on / You know you do it so well) is him asking for the version of her he remembers rather than the one who moved on. He ran into her at the gym and got the news there — "Andas free, bien por ti" (You're single now, good for you) — and the congratulation is as thin as it sounds. He never picks a side: "Es un sí, es un no, dime tú qué vamos a hacer" (It's a yes, it's a no, you tell me what we're doing).