sprite.setFrame

sprite.setFrame sets Frame on a sprite object. It takes id and n.

sprite.setFrame(id, n)

function start() {  const id = sprite.create('/sprites/hero.png', 100, 120);  sprite.setFrame(id, 1);}

sprite.create is there to give the call something to act on; sprite.setFrame is the line that matters. The code sits in start(), which the engine calls once, when the entity spawns.