Please add the following code to functions.php of Wilcity Child (after <?php syntax )

add_filter('wilcity/dashboard/navigation', function($aNav){
    $aNav['affiliate'] = array(
        'name' => 'Affiliate',
        'icon' => 'la la-shopping-cart',
        'redirect' => 'https://google.com',
         'externalLinkTarget' => '_blank' // _self to open link in the same frame
     );
     return $aNav;
});


In case, If you don’t want to show this link on Subscriber dashboard, please use this code

add_filter('wilcity/dashboard/navigation', function($aNav){
    if ( !is_user_logged_in() ) { 
        return $aNav;
    } 
    $oUser = wp_get_current_user();
    if ( in_array( 'subscriber', (array) $oUser->roles ) ) {
        return $aNav;
    } 
    $aNav['affiliate'] = array(
          'name' => 'Affiliate',
          'icon' => 'la la-shopping-cart',
          'redirect' => 'https://google.com',
          'externalLinkTarget' => '_blank'
     );
     return $aNav;
});
 

1. Icon: You can use Font Awesome Or Line Awesome
2. Name: The Name of your Custom Menu Item
3. Redirect: When clicking on Affiliate, it will redirect to this link.