Adding custom icon to icon control in Elementor

icons.php

<?php
/**
 * Adding custom icon to icon control in Elementor
 */
function jet_modify_controls( $controls_registry ) {

	// Get existing icons
	$icons = $controls_registry->get_control( 'icon' )->get_settings( 'options' );

	// Append new icons
	$new_icons = array_merge(
		array(
			'new-icon-1-css-class' => 'icon 1',
			'new-icon-2-css-class' => 'icon 2',
			'new-icon-3-css-class' => 'icon 3',
		),
		$icons
	);

	// Then we set a new list of icons as the options of the icon control
	$controls_registry->get_control( 'icon' )->set_settings( 'options', $new_icons );

}

add_action( 'elementor/controls/controls_registered', 'jet_modify_controls', 10, 1 );