You’re using Foundry, correct? Look at the Typeface stack. You’ll add this to each page and set it to load the Google font and to assign it to one of Foundry’s default fonts.
https://foundry.elixirgraphics.com/documentation/typeface/
If you haven’t yet read about Partials in Stacks, you’ll want to read up on them. They allow you to create a group of stacks that can be used on multiple pages which allows edits to affect multiple pages. The main Foundry stack, the Typeface stack, banners and footers are good candidates for inclusion in Partials.
See partials section here: