This can be done by creating a new automation rule under Admin > Workflows > Automations > Ticket creation 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.
For example:
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.
For example:
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.
Once you add the rules, here's how you can reorder them
https://www.youtube.com/watch?v=Gt2VWBeuBU8&list=PLsYJ3BsyR4qGFujlW0iDtOBOf4IPVsAqt&index=14