Workflow and Custom Fields Builder (dates) in HRM

Hi,

I am able to add a Custom Field (say, expiry dates) to an Employee’s profile. I would also like to have a Workflow where a trigger (send email to an assigned contact) will happen when the Expiry Date is near or happened (like the Birthday trigger) but currently the Custom Field Builder add-on only recognises existing fields in HRM.

Could you advice how I could customise the Workflow add-on for an additional trigger on a Date field like Birthday trigger does? We have many licenses on each employee that expires frequently and we’d like to be notified when they expire (or close to).

Thanks!