Delegate invoke

I want to change a Form control property from a process thread event fire in a class, I have the following code but I received this exception:

the calling thread cannot access this object because a different
thread owns it.

Code:

public partial class main : Window
 {        
    public main()
    {
       InitializeComponent();
    }
 
    public void change()
    {
       label1.Content = "hello";
    }
 
    private void button1_Click(object sender, RoutedEventArgs e)
    {
       nmap nmap = new nmap(this);
       nmap.test("hello");
    }
 }
 
 class nmap
 {
     private main _frm;
     private Process myprocess;
 
     public nmap(main frm)
     {
        _frm = frm;
     }
 
     public void test(object obj)
     {
         string s1 = Convert.ToString(obj);
         ProcessStartInfo startInfo = new ProcessStartInfo();
         myprocess = new Process();
         myprocess.StartInfo.FileName = "C:\\nmap\\nmap.exe";
         myprocess.EnableRaisingEvents = true;
         myprocess.Exited += new EventHandler(myProcess_Exited);
 
         myprocess.Start();
     }
 
     private void myProcess_Exited(object sender, System.EventArgs e)
     {
        try
        {
           _frm.change();
        }
        catch{}
     }
 }
 

Please help me on this, I think delegate invoke must be work

My project is a WPF C# project.

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