How do you know he's a Schedule C filer?  Is that how he filed in 2019?  Is this a new business?  Did someone else help him set up an LLC electing to be taxed as an S Corp, and then he forgot what they said about filing an 1120-S?  

I miss Paul Harvey, and if you're old enough to understand that reference, we should both probably be retired.  

If Congress paid attention to anyone but big contributors, I'd write them suggesting they enact legislation to allow self-employed people to do this.  It would solve a lot of collection problems that IRS must deal with now.