After invited members accept their invitations to join the hub, you can assign Fusion licenses to them. These steps continue from where you (or another administrator) left off in Invite people to a hub (new administrator).
Open the Fusion web client.
Click your profile image in the top-right corner, then select Admin.

Go to the Members tab.

In the Status column, check to see if the recently invited members have accepted their invitations and can be assigned licenses:
To assign licenses in bulk, you can import a list of members using Autodesk account management. Prepare a CSV file with separate columns for first name, last name, and email address, like this:
| First name | Last name | Email address |
|---|---|---|
| John | Smith | jsmith@email.com |
| Jane | Doe | jdoe@email.com |
The import process skips members who already have licenses.
Open the Fusion web client.
Click your profile image in the top-right corner of the page and select My Account, or go to manage.autodesk.com.

In Autodesk account management, go to User Management > By Product.

Click Fusion.

This shows the number of licenses (seats) available, the total number of licenses, and, under Assigned users, people who have had licenses assigned to them so far (if any).
Click Assign users.

In the dialog that appears, choose one of the following ways to assign your licenses:
Use the Assign tab to search for and add users by name or email address.
Use the Import to assign tab to upload a CSV file for bulk license assignment.

Click Assign.
Assigned members now appear in the license list.
Once licenses are assigned, you can optionally Create a project for the members of your hub to work on, or let them do it themselves. It all depends on your organization and how you want to distribute responsibilities.
For more information on setting up Fusion hubs, see this Autodesk blog post.