In fact, I did not expect you will ask this question. uh...it's a really basic question. Anyway, we still can try to solve this question.
In the Score HUD's Script. I wrote this:
# update your score on HUD.
The line here "# update your score on HUD." is a hint to let you update your node Label( or node RichTextLabel, I don't know what node you are using). I mean you have to really update the label's text by using code.
The question here is I don't know your scene tree structure of Score HUD.
So the follwoing is just an ideas, you have to modify it to fix the question.
[In Score HUD's Script]
get_node("Label path").text = "Score: " + str(Global.score)
Modify the "Label path" to fix the question.
P.S. you also can use $ to get node.
If you really don't know how to do that, you can show me the
scene tree structure of Score HUD(using image), so that I can give you more help.