How to autofill lookup field within subform?

How to autofill lookup field within subform?

Hello. I need help using deluge to autofill a subform lookup-field depending on selection made from dropdown field within the subform. Please see details below. Thank you for your help! Chris
  • Main Form: "Add_Customer"
  • Subform: "Programs"
  • Lookup Field Form: "Add_Service"