Marketing Automation : Adding to existing Lead Score

Marketing Automation : Adding to existing Lead Score

I want to be able to add a score to an existing ZMA lead however I can't find the field in the "Fetch Lead" action that contains the existing score.

There is an action for Add lead score, but that's not clear if it overwrites the existing value or adds to it.
eg If I have an existing score of 50 and want to add 10.

When I view the output for Fetch Leads I can see in the raw JSON that there is a field called hub_score but this is not shown in the Flow UI :