You should visit >Settings>Interface and turn on  "Show button View invoice " .


You need PHP code to change url.  This code depends on plugin which you use  to generate invoices


// code for  plugin "Booster Plus"
add_filter('wpo_view_invoice_url', function ($invoice_url, $order_id) {
return add_query_arg( array('order_id' => $order_id, 'invoice_type_id' => 'invoice', 'get_invoice' => '1'), get_home_url() );
}, 10, 2);