Edit the technician - how do I assign them to a site (the same as a requester) so that when they create requests via email they are associated to the correct site?

Example admin/technicians - on this page the site field is not available to be shown/added - for requesters it is available.

If you edit the technician there is no site field - there is a site associated to the department field, but not his site.

I am unable to do anything to his site, in admin/sites to make his dept/site appear in the dropdown for him.

Please advise. I cannot see what determines what sites are available in the department dropdown for a technician.

Thanks,

Dean