You can create a new Employee with Postgraduate loan by entering the details University / College Name and Employee's Employment Start Date. In the process you should use tax code 'NT', set the the last date of payment as the date of leaving and select "yes" for postgraduate loan deduction.

Roadmap:
Employee -> Add New Employee -> Employee Employment Details -> Employee / Pensioner Type -> Select "Student Employee" -> Continue button -> Continue button -> Continue button -> Finish button