Pass variables from Presentation Layer to Logic Layer

I am stuck when I try to make the Logic Layer update the Presentation Layer since I have initialized GUI variables in the Presentation Layer. Still, after that, I couldn't find a way to reach those variables from the Logic Layer. I don't believe that I should make all variables public to reach them.

I have an example here:

• Logic Layer method that updates multiChoicePanel

  public void clearDisplay() {
            if (currentlyDisplayedQuestion.getQuestionType() == QuestionType.MULTI_CHOICE) {
                multiChoicePanel.clearDisplay();
            } 
           else
            ...
        };
  

• Presentation Layer where i have declared multiChoicePanel

    private JQEMultiChoiceQuestionScreen multiChoicePanel;
  

So the question here is how to pass multiChoicePanel to Logic Layer?