Assign service request to support group irrespective site of requester

Assign service request to support group irrespective site of requester

Hi,
We have multi site that's SITE A and SITE B. SITE A include these support group:
  • Infrastructure
  • Servicedesk
  • ERP
  • BPMS
and SITE B include only this support group:
  • Servicedesk

SITE A manage whole request of organization except some easy incident that resolved by a technician (That member of ServiceDesk support group in SITE B) SITE B. 

I want to create service catalog template. In this template I want to define support group that related to every service request but because of I don't known which site's users want to add request, I can't define site and support group. As matter of fact, I want to assign request to related support group after approve request.

Question 1:How should I design below needs so that the following need to be meet?

Thanks
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