When you have created an order or a quote has been converted to an order, access the order from the contact record, in the orders section
Once you are in the order, you want to scroll to the bottom and click the [Payment Plan] Button.
The quick access to the bundle link and any pre-created order forms/checkout are accessible from the "Favourites" link at the top of the page - i looks like a star. If you want any new order forms created or links added, just reach out to support.