How can I make a label display the time remaining countdown of a timer.

Without the relevant code we can;t tell you how to fix this.
But ... this is what I'd do.
Set up a Timer on a half-second interval, and handle the Tick event.
Set up a class level DateTime variable called targetTime.
When you start the countdown, set targetTime to the current date and time plus the interval you want:

targetTime = DateTIme.Now.AddSeconds(30)

And start the Timer.
In the Tick event handler, display the difference:

Dim interval As Integer = (targetTime - DateTime.Now).TotalSeconds

If interval <= 0 Then
    interval = 0
    myTimer.[Stop]()
End If

timerDisplay.Text = interval.ToString()