I think our best bet here is to add a new icon:
add_filter( 'lsi_icons_defaults','lsi_telegram_messenger' );
function lsi_telegram_messenger( $options )
{
$options['telegram-messenger']['id'] = 'telegram-messenger';
$options['telegram-messenger']['name'] = 'Telegram Messenger';
return $options;
}
Adding PHP: https://generatepress.com/knowledgebase/adding-php-functions/
Then add this CSS:
.lsicon-telegram-messenger:before { content: '\e83c'; }
Adding CSS: https://generatepress.com/knowledgebase/adding-css/