change H2 to H1

or if you like to change that globally ( those which are set as Rikard said are not influenced by the snippet – only those headings are changed where the setting is default.)
put this to your child-theme function.php:

function my_avf_customize_heading_settings( array $args, $context, array $extra_args = array()){
  if( 'avia_slideshow' == $context ){
    //  get class of slideshow
    $slider_class = get_class( $extra_args[2] );

    if( in_array( $slider_class, [ 'avia_sc_slider_full' ])){
      $index = $extra_args [1];
      if( '' == $attr['heading_tag'] && 0 == $index ){
        $args['heading'] = 'h1';
      }
    }
  }
  return $args;
}
add_filter( 'avf_customize_heading_settings', 'my_avf_customize_heading_settings', 10, 3 );

see: https://webers-testseite.de/slider-caption/

PS:
avia_sc_slider_full is the fullwidth-slider
avia_sc_slider_fullscreen is the fullscreen slider
avia_sc_slider is easy slider

PPS: this is the better method than mine from https://kriesi.at/support/topic/changing-the-caption-title-on-fullwidth-easy-slider-to-h1/#post-998732
This controls the generation of these headings – the jQuery script only replaces them after the creation process.