CCx is your platform to get the licenses you need. Manage quantities of existing subscriptions can be done using the following method:
When new Microsoft 365 seat-based licenses are ordered – either by adding to an existing subscription or through the purchase of a new subscription, the number of licenses may be reduced in the first 168 hours only, with a prorated refund available.
After Microsoft closes the 168-hour window, Microsoft will not allow cancellation or license count reduction until the end of the subscription term. You can increase your license count at any time mid-term, and each addition of licenses will have its own 168-hour window for license reductions (of the additional licenses only).
You can schedule a reduction mid-term through the Manage renewal functionality and the quantity reduction will take place at the next renewal.
Navigate to the subscription list page

To use the Manage quantity functionality, please navigate to the subscription detail page. On the subscription detail page, you will see a link on the left called Manage quantity. This will present a spinner while a call to Microsoft will bring back the information on what quantity modifications can be made for your subscription.

If you have any licenses that are available for reduction, the number of licenses that can be reduced are displayed with Date & UTC time stamp for ‘allowed until’ closes.
CCx keeps track of the most recent version of the Terms & Conditions (T&C) that you have accepted. If you have already accepted the latest version, you can review them by selecting Version History and no further action is required.
Once done, click Submit changes to complete the quantity change request.
NOTE : A warning message will pop up when attempting to make an immediate change to the subscription (e.g. quantity increase, term/billing frequency, upgrade, etc.) while the subscription has scheduled changes at renewal.
By Microsoft design, ALL scheduled changes are deleted when an immediate change is completed.
If desired, any necessary scheduled changes will need to be re-entered by you after the immediate change is completed.
Microsoft does not allow an increase in quantity for Software Subscriptions or Perpetual products.
If you need additional quantities, you must complete a new purchase.