This can be done by creating a new automation rule under Admin > Automations > Ticket creation tab in Freshdesk.
For assigning all the tickets to one particular agent, you can set the condition to check if 'Priority' is 'Low', 'Medium', 'High', and 'Urgent' (include all 4 priorities), so that the automation runs on all incoming tickets.
Condition: In Tickets > If Priority > is > Low, Medium, High, Urgent
Action: Assign to Agent > Saul
For assigning specific tickets to one particular agent, apply the desired Conditions (can be based on either ticket, contact and company fields) and set up the required Action block.
Condition: Subject contains 'Article Feedback'
Action: Assign to Agent > ABC
This rule will assign all new incoming tickets which have the subject 'Article Feedback' to the corresponding agent.