To assign licenses to Salesforce users, follow 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.
  2. Click the Manage Licenses link next to the Mass File Download name.
  3. Click Add Users.
  4. Choose a view from the drop-down list, or click Create New View to build a new custom view.
  5. 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.
  6. Select users.
    • To select individual users, use the checkboxes. Selected users are listed in the Selected list. When the list includes all users to which you want to assign licenses, click Add.
    • To select all users for the current view, click Add All Users then click OK.