14 day free trial account comes with 5 licenses, 2 are already assigned, one administrator and one field worker. You have 3 licenses left to configure they could be any kind of users: Administrator, Manager or Field Worker.
To learn how to configure a user click here
If your test requires more than 5 licenses please follow this procedure:
Click on "Settings" (1) --> "Subscription" (2)
Change number of Users (3) and click on "APPLY CHANGES" (4)