Adding additional Google Fonts in Vn 3.1.3

Hi Team

Have gone through support and found the code to place into the Child functions.php for adding additional fonts. However, it has no effect?

My Code is

<?php
add_filter( 'avf_google_heading_font', 'avia_add_heading_font');
function avia_add_heading_font($fonts)
{
$fonts['PT Sans Narrow'] = 'PT Sans Narrow:400,700';
$fonts['Rock Salt'] = 'Rock Salt:400';
return $fonts;
}

add_filter( 'avf_google_content_font', 'avia_add_content_font');
function avia_add_content_font($fonts)
{
$fonts['PT Sans'] = 'PT Sans:400,700,400italic,700italic';
$fonts['Rock Salt'] = 'Rock Salt:400';
return $fonts;
}

Any assistance would be appreciated!