How can I hook into and edit the text of a wp_nav_menu tag?

One way to achieve such effect would be to use wp_nav_menu_objects hook.

function modify_home_in_nav_menu_objects( $items, $args ) {
    foreach ( $items as $k => $object ) {
        // you can also target given page using this if:
        // if ( 'page' == $object->object && 2 == $object->object_id ) {
        if ( 30 == $object->ID ) {
            $object->title="<i class="fas fa-home"></i>";
        }
    }
    return $items;
}
add_filter( 'wp_nav_menu_objects', 'modify_home_in_nav_menu_objects', 10, 2 );

PS. Should it really be fas and not fa in there?