@allenbest51 

Example for the 3 green stars

Replace fas fa-star with (for example) myicon

and then add this CSS code to custom css

#wpforo #wpforo-wrap .myicon {
  background: url(Path to your self-created icon);
  background-size: 40px;
  width: 40px;
  height: 40px;
  display: inline-block;
}

to display only the first icon and not all 3

#wpforo #wpforo-wrap .myicon:nth-of-type(2),
#wpforo #wpforo-wrap .myicon:nth-of-type(3){
  display: none;
}

Dashboard > wpForo > Settings > Colors & Styles > Custom CSS

This CSS will help transform any custom icons that we have customized or added, is that correct? But we need to make 11 images and 11 css. Am I understanding this correctly?

#wpforo #wpforo-wrap .myicon {
  background: url(Path to your self-created icon);
  background-size: 40px;
  width: 40px;
  height: 40px;
  display: inline-block;
}

Posted by: @allenbest51

↑

But we need to make 11 images and 11 css.

If you want a self-created icon for each rating level, then yes