how do you unselect the silence feature?

I am replying to my own question because I had this problem and the thread I found, many years old, did not offer one very simple, but --(Apple? 'intuitive design' and 'user friendly'? NOT)-- not easy to figure out in context. That is, the 'silence' PHYSICAL SWITCH on the side of the phone case just north (?!) of the volume buttons. If it is 'off' it looks red; on, black. Apparently it can be easy to knock this thing into the off position; I am using a new protective case which is minimal and great but now that I look with care can see it might permit an odd brush against the inside of my pocket or my hand to change its position.

I had searched and found a long thread in which nobody wrote about this detail; the 'symptom' people were complaining about was that DND was not active; the Always or When phone is locked options HAD TO BE one or the other, and so on. That was my case as well. So I have to end this with a complaint for Apple: this is a fairly obvious feature and also one easy to abuse, accidentally. Is there not a clearer way to implement this?