IF 1 MONTH IS INPUT IN TEXTBOX THEN AUTOMATICALLY SET IN DATETIMEPICKER1 AND DATETIMEPIKER2 THE DATE

You can try for example :

Private Sub TextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles TextBox1.TextChanged
    DateTimePicker1.Value = DateTimePicker1.Value.AddMonths(Convert.ToInt32(TextBox1.Text))
End Sub

You can use AddDays, AddMonths or AddYears to modify the value of your dateTimePicker