1. Select Customers from the navigation pane and Login as the customer.
2. Go to the Account and then Subscriptions and select the relevant subscription.
3. Select the relevant subscription and click the Change button.
4. At the bottom of the page you will see the option to add or remove licenses for the subscription. (Please note that prices shown here are MSRP, and as such discounts will not be shown at this stage - this is so that if the customer is granted access to the panel they see standard pricing).
5. Click Next and Confirm. An order will then be placed and should automatically provision. You will be notified within the customer control panel when the order has been completed.
Known issue
If the next button remains greyed out then you may need to wait a bit longer or add another license and then revert back to the correct amount.