Populate multiple DropDownList using single Model in ASP.Net MVC

I have a ASP.Net MVC5 C# site and I have a controller that I am trying to get a list of my users with role admin and a list of my users with role user.

I have a model that has a list of each. I would like to get a list of each of them so I can use it in my view.

Here is what I have and some of what I tried.

        //models I’m using                                                                      
        public class AdminModel
        {
            public string UserId { get; set; }
            public string Name { get; set; }
        }
        public class UserModel
        {
            public string UserId { get; set; }
            public string Name { get; set; }
            public bool SelectedUsers { get; set; }
            public string AssignToAdmin { get; set; }
        }
        public class AssignRolesModel
        {
            public List<AdminModel> lstAdmins { get; set; }
            [Required(ErrorMessage = "Choose Admin")]
            public string UserId { get; set; }
            public List<UserModel> lstUsers { get; set; }
            public int? AssignToAdmin { get; set; }
            public int? CreatedBy { get; set; }
        }
                                                                                    
        // Controller                                                                              
        public class SuperAdminController : Controller
        {
            private ApplicationDbContext context;

            public SuperAdminController()
            {
                context = new ApplicationDbContext();
            }
                                                                                
            // ASSIGN ADMINISTRATOR
            public ActionResult AssignAdmin()
            {
                var lstAdmins = from users in context.Users
                            from roles in users.Roles
                            join r in context.Roles 
                            on roles.RoleId equals r.Id
                            where r.Name.Equals("Admin")
                            select new AssignRolesModel()
                            {
                                lstAdmins = (users.Id, users.Name),
                            }
                return View();
            }
        }

            @model MVC_TimeSh.Models.AssignRolesModel
            <div class="row">
                <div class="col-md-4">
                    @Html.DropDownListFor(a => a.UserId,
                     new SelectList(Model.lstAdmins, "UserId", "Name"),
                     new { @class = "form-control" })
                    @Html.ValidationMessageFor(a => a.UserId)
                </div>
                <div class="col-md-4"></div>
                <div class="col-md-4"></div>
            </div>

Not sure how to make a list of both of just one in my model.