How to update GUI from FileWatcher event with Task-based Asynchronous Pattern (TAP)

Question

Recently I started learning C# by writing a simple application that watches directory and updates form based on lines written to file in that directory. At some point I was stuck with common InvalidOperationException while trying to update form element from FileWatcher event.

I've searched stackoverflow, and it seems that I should use Task-based Asynchronous Pattern (TAP) in such situations, but I can't figure out which method I should flag as async, and which to start as a Task. There are many related questions on stackoverflow, but none I've found cover all 3 aspects of my application:

• Using FileWatcher
• Updating Form element
• Using TAP

So, what is the best practice to update Form elements from events, fired by FileWatcher if I want to use Task-based Asynchronous Pattern? Or should I use another pattern / another application structure?

Here is a simplified example of my app:

// Form
public partial class FormMain : Form, IDisplayInterface
{
    private CoreClass coreClass;

    public void SetSomeVaue(string value)
    {
        label.Text = value;
    }

    public FormMain()
    {
        coreClass = new CoreClass();
        coreClass.StartFileWatcher();
    }

    private void FormMain_Shown(object sender, EventArgs e)
    {
        coreClass.DisplayInterface = this;
    }
}

// Interface
interface IDisplayInterface
{
    void SetSomeVaue(string value);
}

// CoreClass
class CoreClass
{
    public IDisplayInterface DisplayInterface;

    public void StartFileWatcher()
    {
        FileSystemWatcher watcher = new FileSystemWatcher("C:\Some\Folder")
        {
            NotifyFilter = NotifyFilters.Size
        };
        watcher.Changed += new FileSystemEventHandler(FileUpdated);
        watcher.EnableRaisingEvents = true;
    }

    private void FileUpdated(object source, FileSystemEventArgs e)
    {
        ParseFile(Path.Combine("C:\Some\Folder", e.Name));
    }

    private void ParseFile(string File)
    {
        // foreach (var line in newFileLines)
            ParseNewRecord(line);
    }

    private void ParseNewRecord(string line)
    {
        if (someCondition && DisplayInterface != null)
        {
            // This triggers Exception for accessing FormMain from a thread that did not create it
            DisplayInterface.SetSomeValue(someValue);
        }
    }

}

UPDATE 21.07:

It looks that I got the wrong idea about using TAP everywhere, so I finally did it by invoking a delegate containing my SetSomeVaue method and it works correctly (I hope that is a correct decision).

Thanks for response!