uni-assist e.V. does not cooperate with commercial agencies in or outside of Germany to mediate the placement of applicants at German universities. Some institutions claim to be connected to uni-assist. Official information on applying to uni-assist universities is available only on the websites of the universities and on https://www.uni-assist.de/en/.
A letter which evaluates you positively and recommends you for your course of study.
It is drawn up by your former professors or university teachers.