Depending on the version of Helix Ultimate you have, go to
- Extensions > Templates > Styles
- Click the green Template Options Button
- Then Custom Code. Copy the code at this link and paste it into "Before < /head>" (image)
This will load the font.
If using the font I mentioned above, scroll down to custom css and add the code the the tech person gave you above (I am assuming @Ariba had already determined the style you are trying to insert).
.sppb-addon-tab .sppb-nav a, .sppb-addon-tab .sppb-nav li.active a {
font-family: Byzantine;
}