If my step-son calls for wellness checks more than once, what can I do to him?

You do need to explain more. Do you mean by "wellness checks" having the police come check? Check on whom? On you? If your step-son is genuinely cocerned, why do you feel the need to DO something to him? Even if you do not want or need a wellness check, it doesn't sound like something you should need to retaliate for.

That depends upon whether these wellness checks are needed? We could use some more information from you. If your step-son has reason to worry, doesn't hear from you, and needs to have a check run to make certain you are not unconscious on the floor, then he will likely call. Keep a record of the times he asks for a wellness check. When number three comes along ask the persons making the call (did he call APS or 911) what you can do about the constant calling.
As I said, if you will write more about your questions it will help others to answer you better. Good luck. I hope this is a CARING step-son quite honestly concerned for you; that's actually a good thing, and perhaps you should come up with a.m. and p.m. calls, just a "Hi, how are you" and a "Doing OK; still standing". Many elders have that kind of arrangement going with family or neighbor.

Who is he calling for wellness checks? The Police or Adult protection services (APS)? And why?

Is he calling you and you don't respond? What kind of relationship do you have with him?

How old are you and do you have health problems that he would be concerned about? I know, a lot of questions but hard to reply if we don't have more info.

Perhaps you might need to explain why is he is calling for these "wellness checks" to begin with, before we can properly respond.