To merge order, add this product to the shopping cart as well. With this item in the shopping cart, the system will not charge you for shipping.
Please note that it is not guaranteed; we are not able to merge the order if the order is already in process. Unless we asked you to do so, there will be a risk you need to take that the order may not get merged, and the outstanding order will either need to be refunded or shipped out separately (with the shipping fee being resolved separately).