I have a module called Invoices and within that module I have a field called Service Contract QB Reference and another field called Other Contract QB Reference.  Service Contract QB Reference is a lookup column that corresponds to my Contracts module. Other Contract QB Reference is a lookup column that corresponds to my Other Contracts module.

I have now created another lookup field in my Invoices module called Commissions QB Reference, that corresponds to my Commissions module. But I want this field to be auto-filled based on the information in the Other Contract QB Reference field & the Service Contract QB Reference field. I want it to be auto-filled with whichever one of those fields (Other Contract QB Reference or Service Contract QB Reference) is not empty, as only one will ever contain data.

How can I accomplish this using a workflow?

Thank you.