Scenario 3 is for when you've already been out on a job, and need to schedule a return/completion visit (typically because of having ordered parts, based on a diagnosis as made on the first visit). 

Once again, ServiceDesk quasi-automatically creates and sends an email to your consumer.  It's configured a bit differently for this situation, as follows:

Dear Sir or Madam:

We have received parts as needed for the following repair:

     Job # 72851, ROOMBA CENT VAC
     123 SKY HIGH LANE
     UTOPIA, CA 92629
     949-515-1555  949-516-5656  949-518-6565

We need to make an appointment with you, so our technician can complete this repair.  If you'll simply click on the following link:

It will take you to a page on our website, where you can schedule this visit.

If unable to schedule via that link, please call us at 360-427-6000.

As in Scenario 2, the consumer receives the email, clicks the link, and is taken to an interface on your website that's specifically configured for this situation. 

Please, test again: pretend you're the consumer who's received the email, and click on the link.