Two short stanzas, almost identical, and the speaker is doing something very simple: asking someone to do it again. The laugh comes first, then the smile, and each is treated like a small gift worth having twice. "Sing it again" turns a laugh into music, while "flash it again" makes a smile sound quick and bright, like a light switching on.
What the speaker feels seems like affection, maybe even a little longing. Notice how the lines shift from "The laugh" to "Your laugh." The speaker starts by naming the thing in general, then makes it personal, as if remembering whose it is. Nothing is said about why the speaker wants it so badly, and that gap lets us imagine a few possibilities: a crush, a loved one who has been sad, or someone missed.
The mood is warm, tender and a bit playful. The short lines and repetition feel like a gentle plea, the way you'd ask for a favorite song to be played again.