Oticon Spirit 3 - What does the button do?

Hi All! Just been fiddling with my father’s hearing aids, as he has not been using them for the past few weeks and we are getting frustrated at having to shout at him. They will need a clean and his ears de-waxed! Can someone kindly let me know what the little button does on the top of the plastic housing. I am assuming it cycles through some pre-programmed “modes”?

Thanks for reading