Ethos is a mode of persuasion that uses or mention a source or figure that shows credibility, expertise, prestige or character in order to convince an audience that the information is reliable, valid, and is worth listening.
So, one way to appeal to ethos in one's writing or speech is to use a figure that is known for having expertise, prestige or for having credibility; here's a statement using ethos that best exemplifies it:
"I, the king, the king of the people, assure you that we must continue to fight"
In here, the speaker aims to convince someone to continue to fight via the authority or credibility that the speaker (In this case, a king) has in a certain society.