I once saw a video where the city turned a flight of stairs in to piano keys to make it fun. The majoirty of people then took the stairs over the escalator. You have to find a way to be creative and make taking the stairs more fun or valuable than taking the elevator.
Make the elevator slow. Extra slow. So that people can walk three floors while the elevator makes one.
Or make the elevator doors open at every dust particle that crosses the light barrier.
People will be completely annoyed by that elevator and prefer the stairs.
Not sure it's your business whether they take the stairs or elevator. As much as I wish it was possible to force everyone to be healthy, it's not reasonable.
You can't really make anyone do anything that they don't want to, but I suppose you can always post an "Out of Order" sign on the elevator.
You could put an out of order sign up. Or make up a story to scare the person so they use the stairs.
Have a sign outside the elevator saying 'Take the stairs to avoid awkward silences'
Put a sighn saying out of order use the staires
Put some of that "Do not enter" tape on it :D
Put an out of order sign on the elevator
You may know it better as a "lift".
Offer some type of incintive
are you calling me fat? :P
do something like this
What's an elevator?