Assign it through the license panel

Click on the license button on the sidebar.

Then select which license you want to edit users' rights.

You will be displayed a table with each user who has been granted access to this license.

Use the smart selector to add new users to this list, then do not forget to click on Add user to confirm them in the new list.

When the list of users for this license is ok, just click on Update license to save the changes.

Assign it through the user edition

Click on the Users and Roles button, then on the Users button on the left bar.

Choose which user you want to edit (add or remove a license), then click on its line.

This will display the user edition window.

Go to the license section, where will be displayed the list of all available licenses.
You can assign a specific license to this user by switching on the switch on the right of the license line.

Please note that you must have a classic Mind license to get an Administrator / App Builder / API license.

Then update the user by clicking on Update user.