Currently, it is not possible to assign a different user to Workflow steps when creating a Workflow Template or when adding a Workflow to a Booking.
By default:
Tasks are assigned to the Booking Assignee
Emails are sent from the Booking Assignee
Workarounds:
Once a Workflow Task is created, it can be reassigned to another user
If the Booking is reassigned:
Future Workflow emails will be sent from the new Assignee
You can choose to reassign any incomplete Workflow Tasks to the new