what is the function of this chord

hello guys , i was listening to a song and heard this chord change : Am-G# what is the function of G# after Am and maybe in A minor Scale... ?

Assuming it's just going from the A minor triad (A-C-E) to the G# major triad (G#-B#-D#), I'm not sure if you could justifiably classify this as tonic, dominant or a subdominant.

The root note is the leading tone, which has the dominant function, but the Tritone of D# would essentially weaken or even negate that dominant function, in my opinion. I tend to think of the Tritone as a temporary leading tone to the dominant chord, which would by default lend the Tritone a subdominant function. Finally, the third of the G# major chord, B#, is enharmonically the same as the minor third of the "i" chord, C, lending a hint of tonic function as well (that's probably least important though, as the third scale degree can appear in subdominant seventh chords too). 

Overall, if I HAD to assign it one of those three functions, I'd say it would be dominant because of the root note emphasis on the leading tone. But in reality, I'd consider it more of a colorful chromatic movement that has little to do with classical chord functions.

TLDR: I don't really think it falls into any of the three usual categories, but it sounds interesting. 

Any way to link to the song or moment? I'm curious.

https://mp3mp3.site/start.php?q=5518621_332739025

like this song : nick johnston -atomic mind

First of all, you're a bit off: it's Bb minor to A major.
It's basically playing off the fact that the "#VII" as I'm going to inaccurately call it has a tonic that is the mediant of the dominant chord in the home key.
Such a thing doesn't exist in common practice harmony which is why I used an alternate version of the borrowed chord mark format.

mr i didnt ask that question for this song exactly ! i asked about the movement it can be am-G# instead of Bb minor to A major...