How to resolve this issue?

System.InvalidOperationException: 'The model backing the 'eNtsaRegistration' context has changed since the database was created. Consider using Code First Migrations to update the database (http://go.microsoft.com/fwlink/?LinkId=238269).'

<pre>  // GET://Home/Save
        public ActionResult SaveRegForm()
        {
            ViewBag.Message = "Details saved successfull";
            return View(db.TrainingRegs.ToList());
        }

public class eNtsaRegistration:DbContext
{

    public eNtsaRegistration() : base("eNtsaRegistration")
    {
    }  public DbSet<TrainingRegForm> TrainingRegs { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
    }
}

namespace eNtsaRegistrationTraining.Models
{
    public class TrainingRegForm
    {
        [Key]
        public Guid? Id { get; set; }
        public string Title { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Position { get; set; }
        public string Company { get; set; }

        public string StreetAddress { get; set; }

        public string StreetAddressLine { get; set; }

        public string City { get; set; }
        public string StateProvince { get; set; }

        public int ZipCode { get; set; }

        public string Country { get; set; }

        public string Email { get; set; }

        [Required(ErrorMessage = "This field is required")]
        [DataType(DataType.PhoneNumber)]
        public string CellNumber { get; set; }
        public string DietaryRequirement { get; set; }
    }


    public class RegViewAndRoleViewModel
    {
        public DietViewModel DietMain { get; set; }

        public TrainingRegForm RegForm { get; set; }

       public DropDownViewModel ListCountries { get; set; }
        public RegistrationTrainingForm HomeModel { get; set; }
        public RoleViewModel RoleViewModelData { get; set; }

       
    }

@model IEnumerable<eNtsaRegistrationTraining.Models.TrainingRegForm>

@{
    ViewBag.Title = "SaveRegForm";
}

<h2>SaveRegForm</h2>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.Title)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.FirstName)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.LastName)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Position)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Company)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.StreetAddress)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.StreetAddressLine)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.City)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.StateProvince)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.ZipCode)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Country)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Email)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.CellNumber)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.DietaryRequirement)
        </th>
        <th></th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.Title)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.FirstName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.LastName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Position)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Company)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.StreetAddress)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.StreetAddressLine)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.City)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.StateProvince)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.ZipCode)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Country)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Email)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.CellNumber)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.DietaryRequirement)
        </td>
        <td>
            @Html.ActionLink("Edit", "Edit", new { id=item.Id }) 
            
        </td>
    </tr>
}

</table>