Based on my observation, it appears that the mute button is situated on his nose.
Here's a video tutorial on how to mute: https://www.youtube.com/watch?time_continue=317&v=OWIB5svCfN0&embeds_euri=https%3A%2F%2Fwww.google.com%2F&source_ve_path=MzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMzY4NDIsMjM4NTE&feature=emb_title
