Gallo literally means "rooster" in Spanish. However, in the context of this song and many urban Latin songs, it's used as slang for a "joint" or a marijuana cigarette.
In "Bien High," the artist sings, "Por eso todo el tiempo quiero prenderme un gallo" (That's why all the time I want to light up a joint). This double meaning makes it an interesting and somewhat unexpected word choice, revealing a common slang term used in contemporary Spanish music.
Jasiel Nuñez's "Bien High" is all about that feeling when you're completely smitten, but the person you like seems light-years away. Our singer is down here on Earth, feeling "bien abajo" [really low], while his crush is up on Neptune! He's sending a "chingo de textos" [a ton of texts] but getting no replies, even searching for "los anillos de Saturno" [Saturn's rings] for her. Talk about dedication!
He's trying to cope with the distance, both emotional and literal, by getting "bien high" [really high]. He hopes that by flying high, he can somehow reach her, saying, "Para ver si te alcanzo ahorita que ando volando" [To see if I can reach you now that I'm flying]. It's a fun, relatable take on longing and trying to escape the pain of a one-sided crush, even if it's just in his head.