I want to scroll up the page by using press:Fn+up, but it didnt work on Mac.
There is already a build-in voice command to scroll up - see English Speech Recognition Commands - Voice In
Say scroll up or add a voice command from your phrase to <scrollup>
The function key is a hardware modifier, so you can’t simulate that.
Try one of the following instead
<press:pageUp>
<press:shift+space>
Guide: Action Commands For Keyboard Shortcuts | Voice In Support