To add a service provider to a booking, go to the left menu bar, and click on "Dispatcher" section
Simply drag the booking from either Unassigned or another service provider’s row to the new service provider.
If dragged from the Unassigned row, it will remove it from Unassigned. On the other hand, if the booking is dragged from another service provider, it will remain with the other service provider as well.
Don't forget to save the new assigned schedule :)
Once you save the schedule, you will be prompted if you would like to notify your service provider about their new assignment and if you would like to auto-assign the service providers to all future recurrences of this booking.
You can choose "Yes" or "No" according to your preference and save.