Adding User To Role Using Identity

First Create a viewmodel

 public class ApplicationUserRoleViewModel
    {
        public string UserId { get; set; }

        public string RoleId { get; set; }

 
    }

Create an Empty Controller with name UserAndRolesConroller and add the following actions

  public async Task<ActionResult> AddUserToRole()
        {
            ApplicationUserRoleViewModel vm = new ApplicationUserRoleViewModel();
            var Users = await dbCon.Users.ToListAsync();
            var roles = await dbCon.Roles.ToListAsync();
            ViewBag.UserId = new SelectList(Users, "Id", "UserName");
            ViewBag.RoleId = new SelectList(roles, "Id", "Name");
            return View(vm);
        }

        [HttpPost]
        public async Task<ActionResult> AddUserToRole(ApplicationUserRoleViewModel model)
        {
            var role = dbCon.Roles.Find(model.RoleId);
            if (role != null)
            {
                await UserManager.AddToRoleAsync(model.UserId, role.Name);
            }
            return RedirectToAction("AddUserToRole");

        }

Create a view by clicking in the action and giving the same name

@model WebApplication1.Models.ApplicationUserRoleViewModel

@{

    ViewBag.Title = "AddUserToRole";

}

<h2>AddUserToRole</h2>

@using (Html.BeginForm())

{

    @Html.AntiForgeryToken()

    <div class="form-horizontal">

        <h4>Attendance</h4>

        <hr />

        <div class="form-group">

            @Html.Label("UserId", htmlAttributes: new { @class = "control-label col-md-2" })

            <div class="col-md-10">

                @Html.DropDownListFor(model => model.UserId, null, htmlAttributes: new { @class = "form-control" })

            </div>

        </div>

        <div class="form-group">

            @Html.Label("RoleId", htmlAttributes: new { @class = "control-label col-md-2" })

            <div class="col-md-10">

                @Html.DropDownListFor(model => model.RoleId, null, htmlAttributes: new { @class = "form-control" })

            </div>

        </div>

        <div class="form-group">

            <div class="col-md-offset-2 col-md-10">

                <input type="submit" value="Create" class="btn btn-default" />

            </div>

        </div>

    </div>

}