/** unrequiered checkout fields**/
add_filter( 'woocommerce_default_address_fields', 'customise_postcode_fields' );
function customise_postcode_fields( $address_fields ) {
    $address_fields['postcode']['required'] = false;
    return $address_fields;
} 

add_filter( 'woocommerce_checkout_fields' , 'misha_not_required_fields', 9999 );
 
function misha_not_required_fields( $f ) {
 
	unset( $f['billing']['billing_postcode']['required'] );
	unset( $f['shipping']['shipping_postcode']['required'] );
 
	// the same way you can make any field required, example:
	// $f['billing']['billing_company']['required'] = true;
 
	return $f;
}