This can be found on WP Admin Dashboard > Appearance > Customize > Typography > Headings. If you don’t see this setting on your customizer, you’ll have to activate the Typography module on Appearance > GeneratePress.
Note: If the settings on the customizer setting doesn’t apply on the live size, its possible that there’s a CSS code overriding it. You may have to check WP Admin Dashboard > Appearance > Customize > Additional CSS for any conflicts.
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