Students planning demonstrations for soviet jews asked Lubavicher Rebbe and he advised them against out of fear for the students. They did and eventually helped mln of jews to be freed.
Setting aside the whole prophecy debate, this is simply incorrect.
The Rebbe publicly explained his reasoning for opposing the demonstrations and refuted claims that they were effective.
He was deeply involved in all matters related to the Soviet Union and had numerous sources informing him about developments in Russia, Israel, and the United States.
From a young age, he was engaged in askonus concerning Soviet Jewry and had a far deeper insight into the mindset of Soviet leadership than most.
Many things took place behind the scenes that PR activists didn’t grasp, and the Rebbe publicly elaborated on much of this.
He maintained this position consistently through 1990.
For a comprehensive article on the Rebbe’s position, see here: https://derher.org/wp-content/uploads/69-Sivan-5778-10.pdf
Or Google: Derher “44 sivan 5778”