I assume you're trying to scroll things vertically as items are added to the bottom of the contained label? If that's the case, you can get access to the vertical scrollbar and set it to its maximum value when ever you add text. Here's some sample code snippets...
# Get a reference to the vertical scrollbar
onready var scrollbar = $ScrollContainer.get_v_scrollbar()
# when you add text to the label, just scroll to the bottom...
$ScrollContainer/Label.text += "xxxx"
$ScrollContainer.scroll_vertical = scrollbar.max_value