how was the universal declaration of human rights guaranteed people's rights of assembling peacefully

Human rights are not an invention, but the recognition that, despite all differences, there are basic aspects of human life that must be respected and guaranteed.

The Universal Declaration of Human Rights was drafted in order to safeguard existing rights since there was any indication of rationality in human beings. As such, it did not create or invent rights in its articles, but limited itself to officially writing what, in some way, already existed before its writing.