what is your data center?
for example, take below one.
go to this api site
https://api5.successfactors.eu/sfapi/v1/soap
you will see SFAPI endpoint url and wsdl. save the wsdl file.
https://api5.successfactors.eu/sfapi/v1/soap?wsdl
go to ESR and import the wsdl file into your external definition. check upsert operation.
you will get request and response. you have to keep request fields inside entity.it wont have list of
request fields.
(list of fields you can get it from SF-->Admin tools-->data dictionary-->User entity)
you can play with your request by using soap ui to make sure you are good with request structure.