If you sell, or have sold, packages externally to a client, you can assign a package to a customer through the "Customers" page.
In the customers account, there is a "Package" tab, which allows you to choose what package to assign to the customer:
If you select on the drop down, all available packages in the system should reflect here to select (You can also add multiple packages to the same customer by clicking on the same drop down and choosing the package.):
Any packages assigned to the customer, including both those that you have manually assigned and those that the customer has purchased themselves, will appear in this page and will show you when each one was purchased and how many sessions or minutes remain in each purchased package, this will also allow you to edit the package or remove the package as well: