Auto Assign Ticket

Hey guys, trying to launch this app to people, i need to be able to assign a new request/ticket to certain techs BUT the end user has to choose
ex: location ... USA? UK?
and whatever they choose, is who the ticket will go to.. USA -> TOm
UK -> Steve. etc

anyway i can achieve this? i have been trying with "Groups" but hasnt worked. the end user cant see that field