How to add a custom text to Opulus Sombre

I’m relatively new to wordpress with a basic understanding of CSS, HTML etc. I’ve pretty much finished my site, just adding the last images and final touches. Really want to use a custom font (not google etc) with the Opulus Sombre Theme, having tried several tutorials I still can’t seem to use a custom font for this theme.

I’ve uploaded the font files and tried to change the font family in the pages but can’t seem to get it to work. guessing i need to change the themes CSS but can’t see how.

Any suggestions? if you solve this then you are my hero ??