Automatically set Assignee and a custom field on helpdesk ticket creation

Hi, 

I'm having a lot of trouble trying to work this out. We have a custom `Tenant` field that has a bunch of values of our customers in there. 

I'd like to set up an automation where every time a helpdesk issue is created:
- if we recognise the domain of the email address (EG: @company1.com) then set `Tenant` to company1
- for certain companies, automatically assign a specific helpdesk agent

I've had a look through the workflows repo and can't find how to do this. I can get the reporters email address and do a comparison on that, but I don't know how to assign a specific agent. Hopefully something like “agent with name” or “agent witih email”