How do I remove the hero image on mobile from my home page?

Add the following to Design > Custom CSS.

@media screen and ( max-width: 767px ) {

  [data-section-id="5f5e8390d7bf523730ec3fc7"] .section-background {
  
    display: none;
    
    }
    
  }

Alternately you can put the code in Page Settings > Advanced > Page Header Code Injection for the page.
 

<style>

  @media screen and ( max-width: 767px ) {
  
    [data-section-id="5f5e8390d7bf523730ec3fc7"] .section-background {
    
      display: none;
      
      }
      
    }
    
  </style>

Let us know how it goes.