To assign licenses to Salesforce users, follow the below steps:

  1. From Setup, enter Installed Packages in the Quick Find box, then select Installed Packages to find the installed package that has available licenses.
  1. Click the Manage Licenses link next to the Mass File Download name.
  1. Click "Add Users."
  1. Choose a view from the drop-down list, or click "Create New View" to build a new custom view.
  1. Click a letter to filter the users with a last name that corresponds with that letter, or click All to display all users who match the criteria of the current view.
  1. Select users.
    • To select individual users, use the checkboxes. Selected users are listed in the Selected list. When the list includes all the users to whom you want to assign licenses, click Add. 
    • To select all users for the current view, click Add All Users, then click OK.