Change the font weight via google fonts api

Hi

I would like to add extra bold on some h1-h3 headings. Tried using Avanced Styling and changing the font weight to 800 there but it does not change anything.
By default it seems that Enfold only loads font weight 400 and 600 from google apis.

This is default: https://fonts.googleapis.com/css?family=Open+Sans:400,600
I would like to change it so Enfold load this file instead: https://fonts.googleapis.com/css?family=Open+Sans:400,600,800

Where do I change this without adding extra css code or having to upload the font in full via Custom Font Manager (which sits at 200kb when using zip upload.) The page in total is 287 kb so uploading a font just for additional extra bold and 200 kb extra page size does not make any sense.

Waiting for some help what do to next here =)

BR
Alex