It is not so much about changing the beliefs of a potential voter as modifying their behaviour. In this case giving them enough of a reason to stay at home rather than vote. As the article states:

  > During the campaign, Trump used Facebook to raise two 
  > hundred and eighty million    dollars. Just days before
  > the election, his team paid for a voter-suppression 
  > effort on the platform. According to Bloomberg 
  > Businessweek, it targeted three Democratic 
  > constituencies—“idealistic white liberals, young women, 
  > and African Americans”—sending them videos precisely 
  > tailored to discourage them from turning out for Clinton.
  > Theresa Hong, the Trump campaign’s digital-content 
  > director, later told an interviewer, “Without Facebook 
  > we wouldn’t have won.”