update the set_distribution form on the same path

and use the same method `OrdersController#set_distribution`

app/controllers/spree/admin/orders_controller.rb

@@ -24,7 +24,15 @@ module Spree
         redirect_to spree.distribution_admin_order_path(@order)
       end
 
-      def set_distribution; end
+      def set_distribution
+        return if order_params.blank?
+
+        on_update
+
+        @order.update(order_params)
+        @order.save
+        redirect_to spree.admin_order_customer_path(@order)
+      end
 
       def edit
         @order.shipments.map(&:refresh_rates)

app/views/spree/admin/orders/set_distribution.html.haml

@@ -17,7 +17,7 @@
   = render 'spree/shared/error_messages', :target => @order
 
 %div{"ng-app" => "admin.orders", "ng-controller" => "orderCtrl"}
-  = form_for @order, url: admin_order_url(@order), method: :put do |f|
+  = form_for @order, url: distribution_admin_order_path(@order), method: :put do |f|
     = render 'spree/admin/orders/_form/distribution_fields'
     -# This param passed to stop validation error in next page due to no line items in order yet:
     = hidden_field_tag 'suppress_error_msg', "true"