What is one way to appeal to ethos?

Ethos refers to an appeal to credibility. When an author uses ethos in a text, he tries to persuade the audience of supporting a particular position based on the fact that he is a credible source of information. Therefore, one way to appeal to ethos would be mentioning your credentials or your past experience with the subject. If your readers believe you to be an expert on the subject matter, they will be more likely to be persuaded by your arguments.

the characters in string all have major secrets that they strive to avoid revealing throughout the play.

misty passage from the question