wp_dequeue_style() should help you. You should dequeue style and enqueue your fonts.
wp_dequeue_style('et-core-main-fonts');
wp_enqueue_style('your_fonts_handle', 'path_to_your_fonts');
Or redeclare function with your fonts.
et_core_load_main_fonts() {
$fonts_url = et_core_get_main_fonts();
if ( empty( $fonts_url ) ) {
return;
}
wp_enqueue_style( 'et-core-main-fonts', esc_url_raw( 'path_to_your_style' ), array(), null );
}