D365BC - Subscription model license

We recently purchased a BC license in subscription model. Following the guide of license we can read there might be 1 SA and 3 external accountant.

The guide reports: “Dynamics 365 Business Central includes at no charge, three External Accountant licenses for customers who have external accountants who wish to connect to their Dynamics 365 Business Central application. External Accountant Licenses contain all the same use rights as Dynamics 365 Business Central license except for the following: Access to user set up or admin tasks and any other Dynamics 365 Business Central application.”

I cannot understand how to use these account. My license (1 Essential User) come with 3 full user (1 for the customer ess.user, 1 for SA and 1 for ???).