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:
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.