You can link a past or upcoming one-off session to a client's package by following these steps:
1) Head over to My Clients > [Select client] > Bookings & Packages. If the session is upcoming, locate it in the Bookings section. To view sessions that have also occurred in the past, click the x button on the Today/Upcoming filter:
You can also use additional Filters to find a session:
2) Click on the More options menu beside the session and select Link to package from the options:
3) Select the package you've created for your client:
You should now see the package icon associated with the session: