Assign requests of the users of a site to their own technicians

Assign requests of the users of a site to their own technicians

How can the requests of the users of a site be assigned to the technicians of that site?
Please consider this scenario:
a Company have 50 sites
Site A have 10 users and 1 technician (John)
Site B have 5 users and 1 technician (Kim)
and...up to the end
Site Z
---
How it possible assign all Site A tickets to (John) easily? 
and  assign all Site B tickets to (Kim) and...up to the end?
Like Case Select on programming
CASE
    WHEN SITE A THEN John
    WHEN SITE B THEN Kim
    WHEN conditionN THEN resultN
...

    ELSE result
END;:

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