Schedule an appointment when you don't know who will be have the assignment by doing one of two things: Create a new route or assign it to the Work Pool.

Create a new user with a route name such as, Needs Assignment. (This is called a swing route.) You can assign a work order to this person for when you don't know who is going to be assigned a route. It'll be on the calendar. Once you know who is going to do the work, just reassign it to a real route.

Note This will add an additional charge to your monthly subscription. To see how much go to Settings/Billing & Subscription.

- Or - 

You can assign it to an existing route and use the Work Pool. This will keep the appointment off the calendar. The Work Order will be in the Work Pool until you move it to the calendar and reassign a route to it.