1.If a Ticket is created with Issue Type selected, and the selected Issue Type has assigned staff configured in the Categorization settings then, Ticket will be auto assigned based on the categorization
2.If a Ticket is created without Issue Type and then check in ‘Category’ list, Ticket will be auto assigned based on the staff specified in the ‘Category’ list.
3.If Ticket is not assigned based on the Issue Type and Category, then check for assigned staff in ‘Staff’ list. Ticket will be assigned according to assigned staff in ‘Staff List’
For Staff List
Go to Application Administration in top link bar -> Click Auto Assignment in left navigation link
Refer this article for more detail: Auto-assign Tickets based on selected Category, Issue Type and Requester location - Crow Canyon Software Support