Private Sub LoginButton_Click(sender As Object, e As EventArgs) Handles LoginButton.Click
    If My.Computer.FileSystem.DirectoryExists(MyCityPath + LoginUsername.Text) Then
        'Some code here......
        'This is not completed
    End If
End Sub

Private Sub LoginButton_Click(sender As Object, e As EventArgs) Handles LoginButton.Click
    If My.Computer.FileSystem.DirectoryExists(MyCityPath + LoginUsername.Text) Then
        'Some code here......
        MySecondForm.Target = "Something special"
    End If
End Sub

'...
Public Target As String
'...

Private Sub LoginButton_Click(sender As Object, e As EventArgs) Handles LoginButton.Click
    If My.Computer.FileSystem.DirectoryExists(MyCityPath + LoginUsername.Text) Then
        'Some code here......
        ' Assumes there is a Textbox named Textbox1 on a form named MySecondForm
        MySecondForm.Textbox1.Text = "Something special"
    End If
End Sub