Amiga, date cuenta is a hugely popular cultural phrase that means "Friend, wise up!" or "Open your eyes!". While it literally translates to "Friend, give yourself account," it's used as a wake-up call for someone who is blind to a bad situation, especially in a relationship.
In the song, the narrator uses this viral, meme-worthy phrase to give his friend some tough love. He's telling her to finally see that the guy she's with is no good, perfectly capturing the song's supportive but frustrated tone.
Have you ever had to watch a friend go for the wrong person, even when you knew you were the right choice for them? That's exactly what's happening in this song. Reik and Carin León sing from the perspective of a guy whose friend has just had her heart broken by someone he warned her about. He's not exactly subtle about it, either. The song opens with a direct "Te lo advertí" [I warned you] and he immediately asks, "¿Qué tal te fue con aquel? ... ¿Estás triste?" [How did it go with that guy? ... Are you sad?].
He's the shoulder she cries on, but he's also tired of his friend-zone role. He lays it all out, saying, "Te dije que ese era un pendejo" [I told you he was an idiot] and reminds her, "Te dije que yo era el correcto" [I told you I was the right one]. He even offers a solution: "Si te rompe el corazón, a besitos te lo arreglo" [If he breaks your heart, I'll fix it with little kisses]. The whole song is his blunt, slightly smug plea for her to finally see what's right in front of her, ending with the ultimate advice: "Amiga, date cuenta" [Friend, realize it].