Add one properties AssignedToUser of type int and one unmapped properties AssignedUserName (which will hold the name of that user) of string type in ticket model. So one ticket can assign to only one user at a time. When u fetch a ticket info that time you can set the AssignedToUser value.
For user dropdownlist you can add a SelectListItem in your action method with user information and set it in a VeiwBag to pass the data from controller to view.
Ex: for SelectListItem You can refer to this link.
c# - How can I get this ASP.NET MVC SelectList to work? - Stack Overflow
Check this it may help you.