update Customer DFF through webservice

Hi,

I am creating organization and then creating customer account associated with the organization.

.../foundationParties/CustomerAccountService?wsdl

The technical team has created a field field

Flexfield Name : Parent Number

Flexfield Code: HZ_CUST_ACCOUNTS

Table Column:Attribute_Number20

APIName: ParentNumber

I need to know how to set the the value for the customerAccountService for the flexfield Parent Number and add value to it when I create customer account