How to replace default wordpress navbar link text with font awesome icons

You can use preg_replace. In short, we define a matching $search parameter, then we replace it with what we want.

Here we will search for >Home< and >Listen<.

<?php
/**
* do_action( 'wp_loaded' )
* This hook is fired once WP, all plugins, and the theme are fully loaded and instantiated.
* @link https://developer.wordpress.org/reference/hooks/wp_loaded/
*/
add_action( 'wp_loaded', function() {
  function wp_custom_fontawesome_nav( $subject ) {
    if( ! is_admin() ) {
      $search = [
        '/>Home</', // ... >Home< with the brackets, to be sure to target the right Home word
        '/>Listen</', // ... etc.
        // ... etc.
      ];
      $replace = [
        '><i class="fas fa-play-circle"></i><', // ... Our replacement for Home
        '><i class="fas fa-drum"></i><', // ... Our replacement for Listen
        // ... etc.
      ];
      $subject = preg_replace( $search, $replace, $subject );
      return $subject;
    };
  };
  ob_start( 'wp_custom_fontawesome_nav' );
} ); ?>

Place that in somewhere in your function.php file.