How to default primary assignment , workterm number, latest effective seq default in HSDL template

Summary:

We have a requirement to update assignment Name, Job ,Location, Department with HSDL template . We want prepare a template where HR business user will only enter Person Number ,Effective start date and value for Assignment Name ,Job , Department which needs to be updated.

Currently we need to enter these field values manually in HSDL template Legal Employer, Assignment Number (WorkTerm), Assignment Number (assignment) ,Effective Sequence .

How we can default these values based one existing data in the system.

Please let me know if anyone worked on similar kind of requirement .