Register Helper in functions.php

Hello i trying to register a custom helper to detect if mobile or not, i have this code in functions.php

function is_mobile_handlebars_helper ( $handlebars,$options = null ) {
	// date_i18n.
	// {{my_test_helper 'test value'}}.
	$handlebars->registerHelper( 'is_mobile', function($options = null)  {

		if (preg_match('/(Android|Maemo|iPhone|iPad)/i', $_SERVER['HTTP_USER_AGENT'])) {

		    return $options['fn']();
		} else {

			return $options['inverse']();
		}

	} );
}
add_action( 'lzb_handlebars_object', 'is_mobile_handlebars_helper' );

but is dosen’t work, however this code in the file class-block (inside the plugin)

//custom helpers
	    $this->handlebars->registerHelper( 'is_mobile', function($options = null) {

		    if (preg_match('/(Android|Maemo|iPhone|iPad)/i', $_SERVER['HTTP_USER_AGENT'])) {

			    return $options['fn']();
		    } else {

			    return $options['inverse']();
		    }

	    } );

Work wonderfully, the question is how to fix the code in functions.php to avoid editing core plugin files

Thank you