I cannot delete some file in Movies folder(Meta Quest 2)

I create an app with Unity and I'd like to delete a file in my "Movies" folder. 

However the file is not deleted(File is exist and i'm using File.delete) although my app has permission about external storage read/write.

here's my code. 

string filepath = @"/storage/emulated/0/Movies/myfile.txt";

if(File.Exists(filepath){

        File.Delete(filepath)

}

is there anyway to delete file?