The word subid is the imperative form of subir in the second person plural.
See the full subir conjugation

subir

El mapa dice "subid el sendero, y a la derecha."
The map says, "Go up a trail and to the right."
Bueno, subid el volumen del televisor y escuchen esto.
Well, turn up the volume on your TV and listen to this.
Con mucho cuidado, los tres, subid por las escaleras.
Very carefully, all three of you, head up to the stairs.
Todos los nominados de la corte del baile, por favor, subid al escenario.
All prom court nominees, please come up to the stage.
Si tenéis algo que decir subid aquí.
If you've got anything to say, just step right up.
Bien, estad callados y subid aquí.
All right, just keep quiet and climb up here.
Cuando diga vuestro nombre, subid al escenario.
When I call your name, please come up on stage.
Y tú, tú, tú y tú subid al techo.
And you, you, you and you, up on the top.
Venid, subid a ver a Su Majestad.
Come on up to see His Majesty.
Pues subid, y no perdáis tiempo.
Then come up here, don't waste any more time.
Bueno, damas y caballeros, subid.
Now, ladies and gentlemen, mount up.
Ni idea, subid al caballo.
No idea, get on the horse.
Ahora subid a la cama las dos.
Now up to bed with both of you.
Chicos, subid aquí y presentaos.
Guys, I'd like you to come up and introduce yourselves.
Daos prisa, subid al coche.
Hurry up, get in the car.
Si no os importa, subid al escenario, preciosas.
If you beautiful ladies wouldn't mind joining me on the stage.
No, ellos pueden esperar, subid.
No, they can wait, go up.
Chicas, subid al coche.
Girls, get in the car.
Chicos, subid al coche.
Boys, get in the car.
En ese caso, subid.
In that case, get in.
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