How to use a fancy Sass mixin like this?

Question

css

A piece of code related to setting Heading font sizes.
I don't have enough Sass skill to understand how to change values ​​here? Where do you set font sizes?

// Set headings sizes, line-heights and margins
@each $heading, $properties in $headings {
  #{$heading} {
    @include font-size(nth($properties, 1));
    @include line-height(nth($properties, 2));
    @include margin-top(nth($properties, 3));
    @include margin-bottom(nth($properties, 4));
  }
}

@media screen and (min-width: #{ $max-width + 5 + 'em'}) {
  $leading: $leading-desktop;
  $leading-rem: $leading-rem-desktop;

  @import '../mixins/font-size';
  @import '../mixins/line-height';
  @import '../mixins/margin';

  @each $heading, $properties in $headings {
    #{$heading} {
      @include font-size(nth($properties, 1));
      @include line-height(nth($properties, 2));
      @include margin-top(nth($properties, 3));
      @include margin-bottom(nth($properties, 4));
    }
  }

}