Can't get workflow to update a field upon another field's change

I have created a new date field in the Order form then created a workflow process that should set this field with today's date if a value is selected in another field.

The date field is not being updated and when I click it a calendar pop up appears as it is waiting for the user to input the date.

 I am using CRM 2016, the process is activated and real time.  I am sure I am missing something because I can't see any option in the form assistant that indicates that the field will be automatically filled.

Thanks.

M. Hanno