Logged into Salesforce, under Setup go to Installed Packages

FastCall Setup menu - Installed packages

Find the FastCall package and click Manage Licenses

FastCall Manage Licenses

You will find the number of allowed and assigned licenses. You can add users here.

FastCall - find the number of allowed and assigned licenses or add users here.

If you need to purchases additional licenses, you do so from the App Exchange

Go to the Add AppExchange Apps option to navigate to the AppExchange. You can also navigate from Setup.

FastCall - AppExchange Apps option

Go to MyAccount

https://appexchange.salesforce.com/myaccount

 

FastCall - MyAccount

Click Modify Subscription to Add Users

FastCall - Modify subscription to add users

If you are upgrading from a FastCall package with a Site Wide License , you will need to assign the FastCall licenses to your users. You will also need to assign a FastCall license to the Salesforce Sites Guest User.