WooCommerce - Unset the required property of fields on checkout page.

functions.php

add_filter( 'woocommerce_checkout_fields' , 'xa_checkout_change_required_fields_to_optional' );
function xa_checkout_change_required_fields_to_optional( $fields ) {
     $fields['billing']['billing_address_1']['required'] = false;
     $fields['billing']['billing_address_2']['required'] = false;
     $fields['billing']['billing_postcode']['required'] = false;
     $fields['billing']['billing_city']['required'] = false;
     $fields['billing']['billing_phone']['required'] = false;

     return $fields;
}