The Spanish outfit challenged for a top-four spot last season, but sit in the relegation zone this time around having collected just nine points from their 12 matches.
"I am convinced that the situation will be reversed," Guillen told reporters at a press conference.
"In the last two games there has been an important reaction and, regardless of the results that have not followed, that is the way to go. We need a couple of good results to reverse the situation and recover maximum confidence.
"The coach has all the support. Assessing things midseason is useless. We are in November and the competition is a marathon."
Betis have won just twice in the league this season.