Change Row and Add new row on Datagrid using MVVM

Below is my Xaml and ViewModel class looks like. I try to change the existing row or add new row but both of them doesnt work. When I click empty row, it looses the focus. how I can achieve it directly on Xaml or in ViewModel without using code behind?

<UserControl x:Class="ucCustomer"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:myWPF="clr-namespace:myWPF"
         xmlns:vm="clr-namespace:myWPF.ViewModels"
         mc:Ignorable="d"
       MinWidth="750" MinHeight="650" ><Grid><Grid.DataContext><vm:CustomerVM /></Grid.DataContext><Button x:Name="btnSave" Margin="0,10,10,0" Width="120" Height="25" Content="Save Changes" Command="{Binding btnClick}" HorizontalAlignment="Right" VerticalAlignment="Top"/><DataGrid x:Name="grdData"  AutoGenerateColumns="False" Margin="10,50,10,5"   Style="{StaticResource myDataGrid}"
                  ItemsSource="{Binding Customers, Mode=TwoWay}"><DataGrid.Columns><DataGridTextColumn Header="CustomerId"    Binding="{Binding Path=CustomerId}" Width="50"></DataGridTextColumn><DataGridTextColumn Header="CustomerName" Binding="{Binding Path=CustomerName}" Width="150"></DataGridTextColumn><DataGridTextColumn Header="AccountId"  Binding="{Binding Path=AccountId}" Width="130"></DataGridTextColumn><DataGridTextColumn Header="AccountName"   Binding="{Binding Path=AccountName}" Width="200"></DataGridTextColumn><DataGridTextColumn Header="ModifyDate" IsReadOnly="True"  Binding="{Binding Path=ModifyDate}" Width="130"></DataGridTextColumn></DataGrid.Columns></DataGrid></Grid>

   Namespace ViewModels
            Public Class CustomerVM
                Inherits BaseViewModel
                Implements ICustomerVM

                Private _Customer

    s As New ObservableCollection(Of Models.Customer)
            Private mySaveCommand As ICommand
            Private myLoadCommand As ICommand

            Public Sub New()
                mySaveCommand = New Commands.SaveCustomers(Me)
                myLoadCommand = New Commands.LoadCustomer()
                _Customers = GetCustomers()
            End Sub


            Public Property Customers() As ObservableCollection(Of Models.Customer)
                Get
                    Return _Customers
                End Get
                Set(value As ObservableCollection(Of Models.Customer))
                    _Customers = value
                End Set
            End Property

            Public ReadOnly Property btnClick() As ICommand
                Get
                    Return mySaveCommand
                End Get
            End Property



            Function GetCustomers() As ObservableCollection(Of Models.Customer) Implements ICustomerVM.GetCustomer


                If _Customers Is Nothing OrElse _Customers.Count = 0 Then myLoadCommand.Execute(_Customers)

                Return _Customers
            End Function


            Public Function SaveCustomerstoDB() As Integer
                Dim myContext As New Models.myModelContext
                Return myContext.SaveChanges()
            End Function


        End Class
    End Namespace


    Namespace ViewModels
    Public Class BaseViewModel
        Implements INotifyPropertyChanged

        Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged
        Protected Sub OnPropertyChanged(propertyName As String)
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
        End Sub

        Protected Sub SetAndNotify(Of T)(ByRef field As T, value As T, propertyName As String)
            If Not EqualityComparer(Of T).[Default].Equals(field, value) Then
                field = value
                OnPropertyChanged(propertyName)
            End If
        End Sub

    End Class
End Namespace

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