How to override class of theme in child theme aka get google latin ext fonts

Hi, I have bougth a premium theme at ThemeForest but nobody has answered to my question - they are using Google fonts in the theme, but unfortunately, without latin extended characters and I have no clue how to override them (simply putting it into style.css as import didn't work):

Fonts are loaded with following class (whole file), how do I change it to add latin extended class and how to put it into my child file?

Thanks a lot!
K.