The icon config is located at app/config/icon.php
. Here is were file types are mapped to their respective icons. The mapping is a PHP array where the array key is the file extension (without a preceding dot) and the array value is the desired Font Awesome class names.
return ['icons' => ['7z' => 'fas fa-file-archive','aac' => 'fas fa-music','accdb' => 'fas fa-database','ai' => 'fas fa-image','aif' => 'fas fa-music','apk' => 'fab fa-android','app' => 'fas fa-window','avi' => 'fas fa-video','bak' => 'fas fa-save','bat' => 'fas fa-terminal',// etc...],];