Hi ssv
JA Fit template doesn't call link to that font file directly, it's loaded inside the css file: /templates/ja_fit/fonts/font-awesome/css/font-awesome.min.css so that if a page loads font-awesome, and a element is assigned to use that font, it will be loaded.
So if you want to add preload for this css file, you can use:
<link rel="preload" href="your_site_URL_here/templates/ja_fit/fonts/font-awesome/css/font-awesome.min.css" rel="stylesheet" type="text/css" />
add to the end of file: /templates/ja_fit/tpls/blocks/head.php
Regards